Nudging vaccination against COVID-19: A systematic review and meta-analysis

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Nudging is a new approach that has shown effective results in several areas of health. However, the effectiveness is unclear regarding nudging interventions to improve intentions and behaviors related to COVID-19 vaccination. Methods: We searched PubMed, Web of Science, and Scopus until August 5, 2022. Randomized controlled trials (RCTs) were considered to determine whether nudging improved COVID-19 vaccination behavior and intent. The risk ratio (RR) and 95% confidence interval (CI) were used as pooled measures to assess vaccination behavior. Intention to vaccinate was reported in the narrative synthesis. Results: A total of 15 RCTs involving 167,127 individuals were included. Nudge strategies significantly boosted the COVID-19 vaccine uptake rate (RR: 1.19, 95% CI [1.07, 1.33], p < 0.01). Subgroup analysis showed that there was a weak positive effect on vaccine uptake of social norms (RR: 2.04, 95% Cl [1.61, 2.57]), defaults (RR: 1.32, 95% CI [1.03, 1.69]), and salient reminders (RR: 1.19, 95% CI [1.04, 1.36]). Additionally, the effect of nudging interventions on COVID-19 vaccine uptake weakened over time(p < 0.0001). Most studies (9 of 10) involving vaccination intention outcomes showed positive or partially positive results. Conclusion: Nudging interventions can promote COVID-19 vaccination behavior and intentions, albeit with small magnitude, and need to be combined with other intervention strategies to promote vaccination. Nudge Vaccination COVID-19 Systematic review Figures Figure 1 Figure 2 Figure 3 Introduction Vaccination is a key measure to control the ongoing COVID-19 pandemic. As of November 8, 2022, 68.2% of the world's population had received at least one dose of the COVID-19 vaccine, but vaccination rates vary widely between countries, with only 23.4% of people in low-income countries/areas receiving at least one dose.[ 1 ] Given the need for high vaccination rates to ensure adequate protection of populations and given the role of booster vaccination in combating the threat of new mutations,[ 2 ] there is a need to determine how to effectively increase uptake of COVID-19 vaccine; hence, understanding and addressing the concerns of people who are hesitant about vaccines is key to increasing vaccine intention and uptake.[ 3 ] Vaccine hesitancy (VH) is defined as a "Delay in acceptance or refusal of vaccination despite the availability of vaccination services.”[ 4 ] VH is complex and involves many issues, many of which are specific to the context of COVID-19.[ 5 ] For example, reports exist of a lack of confidence in the efficacy and/or safety of vaccines,[ 6 , 7 ] distrust of the health care system,[ 8 , 9 ] and widespread misinformation or rumors.[ 6 , 10 ] In low- and middle-income countries (LMICs), there are also environmental barriers, such as vaccine production and availability, and distance to vaccine sites.[ 6 , 11 ] A few interventions have been proposed and tested to address VH, including brief written educational interventions (e.g., pamphlets),[ 12 ] use of dialogue, communication, or informational tools.[ 13 , 14 ] Most interventions have focused on changing knowledge, attitudes, and behaviors related to vaccine information and/or safety to address vaccine hesitancy. Although some studies have reported statistically significant improvements in vaccination intention and uptake,[ 15 ] a 2017 literature review noted that many interventions designed to change individuals' perceptions and feelings about vaccination have shown limited effects.[ 16 ] In contrast to change, another range of intervention strategies focused on “nudging” or subtle changes to the design of the environment to encourage specific behaviors.[ 17 ] A nudge is an intervention strategy based on the dual-process model. Such interventions are usually easy to scale and implement at low cost.[ 18 , 19 ] Nudges primarily rely on System 1, which is fast, instinctive, and unconscious, rather than System 2, which is slow and conscious.[ 20 ] This strategy has been shown to be effective in diet change and weight loss[ 21 – 23 ] chronic disease self-management[ 24 ], for example. Regarding vaccination, a field trial showed that text messaging "nudges" encouraged people to receive vaccination against COVID-19.[ 25 ] However, another trial that evaluated the effectiveness of text nudges sent by the Rhode Island Department of Health showed that none of the nudges were effective in boosting vaccination rates for COVID-19.[ 26 ] To date, the effectiveness of nudging interventions is unclear with respect to intentions and behaviors related to COVID-19 vaccination. Therefore, we synthesized the available evidence on the use of nudge techniques in increasing intentions and behaviors associated with the COVID-19 vaccine. The purpose of this review was to assess whether nudge interventions used to improve COVID-19 VH are effective and to provide empirical evidence for researchers and policymakers worldwide. Methods Search strategies This systematic review was developed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Statement 2020 (PRISMA)[ 27 ] We have registered an agreement for this review with PROSPERO (registration number: CRD42022381558). A literature search was conducted of PubMed, Web of Science, and Scopus (end-of-search date: August 5, 2022). We included the Medical Subject Headings (MeSH): “behavioral control,” “vaccination,” “vaccines,” “vaccination coverage,” “SARS-CoV-2,” and “COVID-19,” and the following non-MeSH terms: “behavioral intervention,” “behavioral strategy,” “nudge,” “nudging,” and “immunization rates” using Boolean operators “AND” and “OR” to combine keywords into the final search string (Supplementary Table S1). We scanned a list of references from relevant systematic reviews to identify randomized controlled trials that met our inclusion criteria. Eligibility Criteria Given that people of all ages can be vaccinated, we are not imposing any restrictions at the population level. Thaler and Sunstein[ 17 ] defined a nudge as “any addition to or modification of the environment that influenced consumers in a predictable way, without changing economic incentive;” however, this definition is difficult to implement. Hausman and Welch added more detail to this definition by emphasizing that a “nudge” represents an attempt to prevent irrational choices by actively changing behavioral biases.[ 28 ] We used this definition to exclude interventions that were not consistent with nudge strategies. The eligibility criteria are shown in Table 1 . Table 1 Inclusion and exclusion criteria. Criterion Inclusion Exclusion Population and sample General population, reflecting all vaccination target groups and all stakeholders involved in vaccination decisions Literature focus 1. Full-text papers and reports, peer reviewed articles. 2. Interventions belonged to the nudge category 3. The results were the impact of nudging on COVID-19 vaccine uptake and/or vaccination intention 4. The study design was a RCT 1. Articles that are abstract only and/or lack retrievable full text 2. Literature reviews, editorial letters and comments, theoretical/background papers 3. Interventions not attributed to a nudge strategy langue English Study Selection, Data Extraction, And Quality Assessment The following information was extracted and validated for the included studies using a standardized Excel form: Study and participant characteristics (e.g., authors, publication date, country, sample size, and population description), intervention characteristics (study group, control group description, intervention strategies, time points), and study outcomes (vaccination uptake, intention to vaccinate). If the outcome of a study was measured at multiple time points, we selected the outcome that the study authors specified as the primary outcome; if this was unclear, we averaged the results over time. For multi-arm studies, data from each arm with different nudging elements were extracted. We assessed the risk of bias of the included studies using the Cochrane Risk of bias tool.[ 29 , 30 ] For each study, each criterion was scored as low risk, unclear risk, or high risk of bias. Data Synthesis And Analysis Risk ratios (RRs) and 95% confidence intervals (CIs) were used to calculate the pooled effect size. We considered the different nudging interventions in each study and combined data using a random-effects meta‐analysis of the number of people receiving immunizations. When summary statistics were not provided, we calculated RRs based on the number of events and individuals in each intervention group. Conversely, if the total number of events was missing, we estimated values using the summary statistics and their confidence intervals. Publication bias was evaluated using funnel plots, and Egger's test and Begg's test were used to evaluate the asymmetry of funnel plots. Significant publication bias was considered present if p < 0.05. Sensitivity analysis was conducted to assess the stability of the study using the leave-one method Subgroup analysis was performed at different time points to evaluate the outcomes (< 4 or ≥ 4 weeks), comparison (no intervention/usual care or other intervention), study location (US or Europe), year (2021 or 2022) the proportion of persons vaccinated (≥ 70% or༜70%) and types of nudge. Nudging interventions were summarized drawing on the MINDSPACE framework (Defaults, Salience, Messenger, Incentives, Ego, Priming, Commitment, Affect, and Norms) and Sunstein's list (default rules, simplification, increases in ease and convenience, uses of social norms, warnings, disclosure, pre-commitment strategies, reminders, Elicits the intention to act and informs people of the nature and consequences of their past choices).[ 31 , 32 ] We performed a meta-regression to assess the validity of the hypothesis that RR reduction was proportional to the intervention’s time-lapse. All statistical analyses were performed via R 3.6.2. Beyond vaccination uptake, conducted a narrative synthesis of other outcomes related to vaccination (vaccination intention). Results The search identified 2,596 articles ranging from January 1st, 2020, to August 5 th, 2022 (Fig. 1 ), of which 15 peer-reviewed articles were included in the final analysis (Table 2 ). Table 2 Characteristics of the included randomized controlled trials (RCTs). Author (Year) Participants Country Arm Interventions Comparison Time points outcome Dai(2021) N = 93354 (patients registered at UCLA health) US 5 Basic reminder/Ownership reminder No text message 4 weeks Vaccination uptake (+) Bartoš(2022) N = 2101(general population adults) Czekh 2 Consensus condition No information 2 weeks/4 months Intention to vaccinate (+) and Vaccination uptake(+) Sasaki(2022) N = 1595(25–34 young and 65–74 elderly) Japan 4 social-comparison/gain-framed social influence/loss-framed social influence Basic Information 3 days Intention to vaccinate(0) Tentori(2022 N = 2000(50–59 adults) Italy 2 opt-out group OPT-IN group 3 weeks Vaccination uptake (+) Campos(2021) N = 8286(18–49 adults) Sweden 5 Incentives/Social impact/Information/Arguments Basic reminder After intervention /4 weeks Intention to vaccinate (0) and Vaccination uptake (0) Santos(2021) † N = 9723(Employees registered at Geisinger Health System) US 3 social norms/reframing risks Delayed control 3 days Vaccination registration (+) Ashworth(2021) N = 3048(general population) US 9 Private benefit/ Social benefit/ Economic benefit/Vaccine safety No information After intervention Intention to vaccinate (+) Mehta(2022 N = 16045(patients visit at a Penn Medicine primary care provider) US 9 2× 4 design; Call Back/ In-Bound Call + Standard Msg/ Clinician Endorsement/ Scarcity/ Opt-Out Framing outbound call only 1 month Vaccination uptake (-) Patel(2022) N = 2000(Ascension Associate Employee.) US 2 Text message Usual care 2 weeks Vaccination uptake (+) Jensen(2022) N = 890(general population adults) US 5 Video-based messages: safety/ social norm/ response efficacy/ self-efficacy Basic Information After intervention Intention to vaccinate(+) Liu(2022) N = 1926(general population) China 7 Conventional Opt-out/ Improved Opt-out OPT-IN group After intervention Intention to vaccinate(0) Motta(2021) N = 7064(general population adults) US 12 3 × 2 × 2 design; personal health risks/collective public health consequences of not vaccinating/ economic costs + lay source/ expert sources + Highlighting the rigors of clinical trials/ Not highlighting the rigor of clinical trials No information After intervention Intention to vaccinate(0) Freeman(2021) N = 16455(general population adults) UK 10 collective benefit (3 conditions)/personal benefit/seriousness/safety, direct/safety, indirect/collective and personal benefit/full combination Safety and effectiveness statement After intervention Intention to vaccinate (0) Burger(2022) N = 1324(general population) Germany 4 Debunking/ Benefits/ Facilitation No information After intervention Intention to vaccinate (-) Gong(2021) N = 1316(general population adults) China 4 Gain-Framed/ Loss-Framed/ Altruistic Messages No information After intervention Intention to vaccinate (+) * The sign in parentheses indicates whether the results supported the effectiveness of the respective intervention (+), provided evidence of lack of effectiveness (−), or reported mixed results (0). † The primary outcome of the study was vaccination registration, but given that the study population was employees of a large health system and that there were employee-only vaccination clinics with approximate vaccination registration and actual vaccination numbers, we treated the outcome as vaccine uptake. A total of 167,127 people were included, predominately from the general adult population. Most of the included studies continued for 1 month after the intervention,[ 25 , 33 – 45 ] except one study, which continued for 4 months.[ 46 ] All studies were conducted in high-income or upper middle-income countries (USA (n = 7),[ 25 , 33 , 35 , 37 , 39 – 41 ] China (n = 2),[ 38 , 45 ] Czech Republic (n = 1),[ 46 ] Italy (n = 1),[ 43 ] Sweden (n = 1)[ 44 ], Japan (n = 1),[ 42 ] UK (n = 1),[ 34 ] and Germany (n = 1).[ 36 ] Seven studies incorporated control groups that received no intervention or usual care.[ 25 , 33 , 36 , 37 , 39 , 45 , 46 ] The risk of bias for all included studies is summarized in Supplementary Fig. 1. Full details of the risk of bias assessment for each study are provided in Supplementary Table S2. Of the 15 randomized controlled trials included in the evaluation, 10 were rated as of high quality and none as of low quality. A lack of allocation concealment description and clear blinding were common factors that limited the quality of the studies. Characteristics Of Nudge Interventions After considering the operability of nudge strategies in the intervention studies, we identified a total of six types of nudging interventions employed across the selected studies (Table 3 ). Almost all of the included studies (12 of 15) were multinudge element interventions[ 25 , 33 – 36 , 38 – 42 , 44 , 45 ]; nine studies applied the nudge intervention of a salient reminder,[ 25 , 34 – 37 , 39 – 41 , 44 ] seven studies applied an information framework,[ 33 , 34 , 36 , 39 , 42 , 44 , 45 ] three studies applied messaging,[ 33 , 35 , 46 ] three studies applied social norms,[ 40 – 42 ] two studies applied defaults,[ 38 , 43 ] and one study applied financial incentives.[ 44 ] Table 3 Summary of nudging interventions. Type of nudging Rationale Nudging-based approaches employed in the included studies Salient reminder A reminder can ensure that people can act immediately on the salient information that is provided in that particular moment.[ 31 , 32 ] 1. Use familiar and trusted sources (e.g., health centers, large survey companies, etc.) to provide vaccination reminders/recalls;[ 25 , 35 , 36 ] 2. Write down arguments that could best convince another person to get vaccinated;[ 44 ] 3. Highlighting the safety and efficacy of COVID-19 vaccine;[ 34 , 44 ] 4. Juxtaposing the risk of the vaccine with the risk of COVID-19;[ 40 ] 5. Highlighting the safety and rigor of COVID-19 vaccine clinical trials;[ 39 ] 6. SMS highlights the limited availability of vaccines;[ 35 ] 7. Description of vaccine retention for participants, highlighting vaccine ownership;[ 25 , 35 , 37 ] 8. Video-based reminders and recalls to highlight vaccine safety, efficacy or vaccination retention information, convenience, etc;[ 25 , 41 ] 9. Receiving information debunking vaccination myths increases the intention to get vaccinated.[ 36 ] Financial Incentives Incentives, both tangible and intangible, can increase favoured behaviour.[ 31 ] 1. Provide monetary incentives to increase vaccination intentions and actual uptake.[ 44 ] Messenger Changing the source from which the information is delivered (eg, a trusted peer or a doctor) can alter the level of emphasis on the information.[ 31 ] 1. Provide the true view held by physicians to correct misunderstandings about vaccine uptake);[ 46 ] 2. Clinicians provide vaccination advice;[ 35 ] 3. Expert (vs. lay) sources of vaccine support information.[ 33 ] Information Framework The same outcome is perceived differently when the benefits gained (eg, lives saved) and losses avoided (eg, deaths avoided) inform the message.[ 31 ] 1. Gain-framed messaging (describing benefits of receiving vaccines)[ 36 , 45 ] versus loss-framed messaging (describing the cost of not receiving the vaccine);[ 45 ] 2. Make a list who would benefit from the participant getting vaccinated;[ 44 ] 3. Describe the private[ 34 , 39 ], social[ 34 , 39 , 42 ], and economic benefit[ 39 ] of vaccination; 4. Describe the personal[ 33 ], Economic[ 33 ], and Collective[ 33 , 42 ] Health Risk Frames); 5. Altruistic messages to motivate people to accept COVID-19 vaccination.[ 45 ] Social Norms People tend to behave in ways that are consistent with their perceptions of the social environment and widely accepted behaviors in their peer groups.[ 31 , 32 ] 1. Based on emails, videos, etc. indicating that a large proportion of people around or colleagues have chosen to be vaccinated to improve vaccine uptake).[ 40 – 42 ] Defaults Changing whether something is the default option versus requiring explicit opt-in can change behaviour.[ 31 , 32 ] 1. Vaccination appointment has been scheduled (with opting out possible);[ 43 ] 2. Opt-out policy and its improvements(different information was provided for the opt-out policy).[ 38 ] Effects Of Nudging Interventions Various outcome measures were used to assess the effect of nudging interventions. The most frequent were vaccination uptake (n = 7)[ 25 , 35 , 37 , 40 , 43 , 44 , 46 ] and intention to vaccinate (n = 10).[ 33 , 34 , 36 , 38 , 39 , 41 , 42 , 44 – 46 ] As can be seen from Table 2 , half of the articles reported positive effects (n = 7),[ 25 , 37 , 39 , 40 , 43 , 45 , 46 ] while other articles reported partially positive effects with mixed or inconclusive overall results (n = 6).[ 33 , 34 , 38 , 41 , 42 , 44 ] Significantly, two articles identified that nudging interventions has no effect.[ 35 , 36 ] These negative findings involved nudges that were divided into different texts plus inbound/outbound call groups[ 35 ] and a message intervention debunking vaccination myths or highlighting benefits.[ 36 ] Detailed characteristics of all nudge interventions are described in Supplementary Table S2. Impact Of Nudge Interventions On Vaccine Uptake Seven studies reported vaccine uptake results, with a total of 131,719 people included.[ 25 , 35 , 37 , 40 , 43 , 44 , 46 ] Five studies found statistically significant increases in vaccination uptake compared with control groups,[ 25 , 37 , 40 , 43 , 46 ] one study[ 44 ] reported mixed results, and one study[ 35 ] identified no effects from the nudging intervention. The pooled results showed that vaccine uptake was significantly higher in the nudging intervention group compared to the control (RR: 1.19, 95% CI [1.07, 1.33], p < 0.01, Fig. 2 ). The heterogeneity was 93%, and a random-effects model was adopted. The funnel plot appeared to be asymmetric (Supplementary Figure S2), but Begg's test (p = 0.195) and Egger's test (p = 0.590) revealed no major publication bias in the included articles. Sensitivity analyses using the leave-one-out method did not significantly alter the overall outcome of vaccine uptake (Supplementary Figure S3 ) . The results of the subgroup analysis are shown in Table 4 and Supplementary Figures S4–S9. The nudging intervention appeared to have a greater effect on vaccine uptake in the group with follow-up < 4 weeks (RR: 1.59, 95% CI [1.16, 2.19]) than in the group with follow-up ≥ 4 weeks (RR: 1.12, 95% CI [1.05, 1.20]), although the difference was not significant. When we stratified, by comparison, the difference in vaccine uptake between the trial and control groups was significant only when the control was no intervention/usual care. Nudging appeared to have a more pronounced effect on vaccine uptake when the COVID-19 vaccine was available early and when general vaccination rates were low (i.e., literature published in 2021 or when the control group had vaccination rates less than 70%). Regardless of whether the study was conducted in the United States or Europe, the boost to vaccination uptake was significant (p 0.05). All types of nudge interventions except the information framework had a weak positive effect on vaccine uptake (p < 0.05). Among the six nudge types, a stronger effect on vaccine update was observed for social norms (RR: 2.04, 95% Cl [1.61, 2.57]), defaults (RR: 1.32, 95% Cl [1.03, 1.69]), and salient reminders (RR: 1.19, 95% Cl [1.04, 1.36]). Table 4 Subgroup analysis of nudging intervention on vaccine uptake. Intervention type Outcome: received immunizations Illustrative comparative risks* (95% CI) Relative effect (95% CI) No of participants (studies) Assumed risk Corresponding risk Without intervention With intervention Nudge(summary) 203 per 1000 242 per 1000 (217 to 270) RR 1.19(1.07 to 1.33) 131,719(7) Time points Nudge(≥ 4 weeks) 215 per 1000 241 per 1000 (226 to 258) RR 1.12(1.05 to 1.20) 118,196(4) Nudge(< 4 weeks) 74 per 1000 118 per 1000 (86 to 162) RR 1.59(1.16 to 2.19) 13,523(3) comparsion No intervention/usual care 147 per 1000 179 per 1000 (168 to 191) RR 1.22(1.14 to 1.30) 96,974(3) Other intervention 415 per 1000 486 per 1000 (398 to 593) RR 1.17(0.96 to 1.43) 34,745(4) Study location US 131 per 1000 168 per 1000 (140 to 199) RR 1.28(1.07 to 1.52) 120,965(4) Europe 668 per 1000 695 per 1000 (681 to 708) RR 1.04(1.02 to 1.06) 10754(3) Year 2021 201 per 1000 255 per 1000 (219 to 297) RR 1.27(1.09 to 1.48) 90086(3) 2022 239 per 1000 258 per 1000 (246 to 272) RR 1.08(1.03 to 1.14) 21622(4) Proportion of Vaccination ≥ 70% 715 per 1000 744 per 1000 (729 to 758) RR 1.04(1.02 to 1.06) 8797(2) ༜70% 131 per 1000 169 per 1000 (144 to 197) RR 1.29(1.10 to 1.50) 122922(5) Nudge types Salient reminder 173 per 1000 206 per 1000 (180 to 235) RR 1.19(1.04 to 1.36) 118779(5) Messenger 485 per 1000 519 per 1000 (485 to 548) RR 1.07(1.00 to 1.13) 5930(2) Defaults 99 per 1000 131 per 1000 (102 to 167) RR 1.32(1.03 to 1.69) 1957(1) Financial incentives 716 per 1000 759 per 1000 (723 to 788) RR 1.06(1.01 to 1.10) 3909(1) Information Framework 716 per 1000 737 per 1000 (709 to 766) RR 1.03(0.99 to 1.07) 3892(1) Social Norms 32 per 1000 65 per 1000 (52 to 82) RR 2.04(1.61 to 2.57) 6376(1) Meta-regression analysis (Fig. 3 ) indicated a nonsignificant association between vaccination and passage of time within 4 months (p = 0.095), but only one study exceeded 1 month; therefore, we excluded this study to explore a 1-month trend. The results after exclusion showed that within 1 month, the increase in vaccination was inversely associated with the passage of time (p < 0.0001). Impact Of Nudge Interventions On Vaccine Intention Among the 10 studies that considered intention to vaccinate as the primary outcome of interest,[ 33 , 34 , 36 , 38 , 39 , 41 , 42 , 44 – 46 ] three studies found statistically significant increases in vaccination intention compared with control groups.[ 39 , 45 , 46 ] More than half of the studies (6 of 10) reported mixed results regarding vaccination intention among study participants,[ 33 , 34 , 38 , 41 , 42 , 44 ] and one study identified no effects of the nudging intervention on vaccination intention (Table 2 ).[ 36 ] Table 5 summarizes the characteristics of the vaccine intentions for outcome studies. The supplementary table S2 provides a more detailed view of each study. Table 5 Characteristics of nudge interventions on vaccination intentions. Reference Types of nudging Implementation details Findings Bartoš et al[ 46 ] Messenger Consensus condition, participants were provided with a summary of the survey among medical doctors, including three charts that displayed the distribution of doctors’ responses regarding their trust in the vaccines, willingness to get vaccinated themselves and intentions to recommend the vaccine to patients Public misconceptions about what doctors think about COVID-19 vaccines are common, and correcting them will boost vaccination intentions. Sasaki et al[ 42 ] Information Framework/ Social Norms The three groups were randomly assigned peer information: comparison, influence-gain, and influence-loss. The effect of each piece of information on vaccination intentions was compared The influence gain nudge was effective in increasing the number of older adults who newly decided to vaccinate, but had no boost for younger adults who were less willing to vaccinate at baseline. Campos et al[ 44 ] Financial Incentives/ Salient reminder/Information Framework The effect of a small cash reward, around US $ 24, was compared with the effect of several behavioral nudges. The nudge measures are social impact condition, arguments condition and information condition Financial incentives significantly increased vaccination intentions and coverage rates, while other incentives increased vaccination intentions but had little effect on vaccination rates Ashworth et al[ 39 ] Information Framework/ Salient reminder "Private benefit", "social benefit", "economic benefit" and "vaccine safety" information individually and in combination to examine the impact on vaccine intent, Participants were randomly assigned to one of nine informational treatments Several forms of public information can increase vaccine intent, but messages that emphasize individual health benefits have the greatest impact. Jensen et al[ 41 ] Salient reminder/ Social Norms Four different treatment videos were made based on planned behavior theory, (i) attitudes about vaccine safety, (ii) normative beliefs about subjective social norms of vaccination, (iii) attitudes about vaccine efficacy (response effect), and (iv) perceived behavioral control over vaccination (self-efficacy). Short video encouraging messages that address specific issues with COVID-19 vaccines increase vaccination intentions Liu et al[ 38 ] Defaults There are seven vaccination policies, including an opt-in policy with no default, an opt-out policy with vaccination as the default, and five improved versions of the latter, including Social Norm, Transparency, Education, Feedback and Opportunity Opt-out policies and their improvements (with the exception of opt-out transparency) increase the willingness to vaccinate. Motta et al[ 33 ] Information Framework/Messenger Respondents were randomly assigned to read a short pro-vaccine opinion article, depending on (i) the framework (individual health risks, collective public health consequences and economic costs of not vaccinating), (ii) the source of information (i.e. lay versus expert sources), And (iii)the presence or absence of pre-bunking information highlighting the rigors of clinical trials prior to reading the opinion piece. Regardless of the source, information that emphasizes the individual health risks and collective health consequences of not vaccinating can significantly increase Americans' intention to get vaccinated. The economic cost framework had no significant effect on vaccine intent Freeman et al[ 34 ] Information Framework/ Salient reminder Participants were randomly assigned to ten information conditions stratified by their level of vaccine acceptance (willingness, skepticism, or strong hesitation). Condition 1 was the control group, whose text included safety and efficacy claims taken from the NHS website. Three conditions address only collective interests (conditions 2, 3 and 4), one individual interests only (condition 5), one combines collective and individual interests (condition 9), one concerns the severity of the pandemic (condition 6), two concerns security issues (conditions 7 and 8), and the final condition addresses the complete combination of interests, Seriousness and safety issues (Condition 10) In populations that are very hesitant about COVID-19 vaccines, the provision of information of individual benefit reduced indecision to a greater extent than information of collective benefit. Burger et al[ 36 ] Salient reminder/Information Framework Assess whether debunking vaccination myths, highlighting the benefits of vaccination, or sending vaccination reminders will reduce hesitation No increase in the willingness to vaccinate, regardless of the information provided Gong et al[ 45 ] Information Framework An online survey experiment consisting of a control group (exposed to non-framing information) and three experimental groups (exposed to gain framing, loss framing, or altruistic information) was designed to assess vaccination intentions People exposed to the gain frame, loss frame, or altruistic messages were more likely to be vaccinated against COVID-19 than those exposed to non-frame messages. In addition, the loss of frame information had a more significant effect on vaccination intentions than the other two types of information. There was mixed evidence regarding the effectiveness of nudging for increasing vaccination intentions for different information frames. A randomized controlled trial in Japan[ 42 ] evaluated the effect of different peer messages on vaccination intentions; only gaining frame messages were effective at increasing the number of older adults who newly decided to get vaccinated. In contrast, a study in China showed[ 45 ] that people exposed to lose frames showed higher intentions of obtaining a COVID-19 vaccine compared to gain frame messages. Ashworth et al.[ 39 ] defined three messages emphasizing different benefits of the vaccine and one emphasizing vaccine safety, and evaluated the impact on vaccine intentions of transmitting the four messages individually and in combination. The results suggested that although safety concerns were the main reason for hesitation regarding the COVID-19 vaccine, the group exposed to the vaccine safety message did not exhibit significantly increased vaccination intentions. The message emphasizing personal health benefits had the greatest impact. An RCT[ 33 ] conducted in the United States prior to the introduction of the COVID-19 vaccine found that intention to receive COVID-19 vaccination increased significantly when information was tailored to individual health risks, the consequences of not receiving the vaccine, and when these framing messages came from medical experts. In the United Kingdom, a randomized controlled trial[ 34 ] similarly showed that individuals who were strongly hesitant about the COVID-19 vaccine were influenced more effectively by personal benefit messages than were those who received collective benefit messages. In addition to information frames, other types of nudges also led to different results. A study in the Czech Republic[ 46 ] focused of a facilitation intervention on changing the messengers assigned to convey vaccine-related health messages. A study in the US[ 41 ] adopted a short video of c. 30 seconds for the specific problem of COVID-19 vaccine, Campos et al.[ 44 ] used incentives as a mechanism for behavior change. In each of these studies, nudge measures all increased vaccination intention to varying degrees, but it is worth noting that in Campos et al., salient reminders and information framework nudge measures increased intention to vaccinate but had a small and statistically insignificant effect on vaccination rates. Mixed results were also seen in a randomized trial in China,[ 38 ] in which investigators considered the use of defaults and refined defaults in the unvaccinated population to increase intention to receive the COVID-19 vaccination. Opt-out policies increased the intention to receive vaccination, but none of the refined versions resulted in significant changes in participants' intention to vaccinate compared to the traditional opt-out condition. A German registry trial showed[ 36 ] that willingness to vaccinate did not increase regardless of whether the information provided debunked vaccination myths or emphasized the benefits of vaccination or sent vaccination reminders. Discussion This systematic review is the only synthesis of available evidence on how nudging affects intentions and behaviors related to COVID-19 vaccine uptake. Overall, data from seven randomized controlled trials were pooled to show that the nudge strategy slightly increased COVID-19 vaccine uptake (RR: 1.19, 95% Cl [1.07, 1.33]). These increases were more pronounced in the short-term (< 4 weeks), with a no intervention/usual care control group, in the US, when vaccine the vaccine had recently become available (year = 2021 and proportion of the vaccinated population vaccinated < 70%), and for the nudging type of social norms. Nine of the ten studies involving vaccination intention outcomes reported positive or partially positive results. These findings indicated that low-cost and short-duration nudges may be an effective way to mitigate COVID-19 vaccine hesitancy. A previous systematic review found that nudging interventions showed the potential to increase vaccine confidence and uptake [ 47 ]; this is consistent with our results. Although our study showed that nudging measures can only foster small improvements in vaccination update, given the generally easy and low-cost implementation of nudges,[ 17 , 31 , 48 ] they represent a practical approach that can be applied to large populations. Available evidence suggests that even small gains, when applied to large populations, can represent the vaccination of millions of people.[ 25 ] In the studies included in the present review, some control groups also received interventions; for example, some studies used basic information or simple reminders with the control group.[ 41 , 42 , 44 ] In our analysis, by comparing no-intervention control groups with control groups that received other interventions, the pooled results suggested that adding targeted nudges to existing interventions may be an important consideration to improve vaccine behavior and intentions. In addition, there were differently worded interventions in the included multi-arm studies. In a study of more than 90,000 people in California,[ 25 ] researchers found that “ownership” reminders boosted vaccination rates by approximately 1.1 percentage points more than did basal reminders. However, in Liu et al.,[ 38 ] none of the improved versions resulted in a significant change in participants' willingness to receive vaccination compared to the traditional opt-out condition. Some studies also suggested that using a nudge intervention with groups that already have ambivalent feelings about vaccination may be counterproductive.[ 49 , 50 ] Therefore, subtle changes, including in wording based on original nudges, require careful design and further study. A key finding of our analysis was that the effect of the nudging intervention on COVID-19 vaccine uptake gradually decreased over time, and the results presented in the follow-up time point subgroup appeared to corroborate such findings. Some studies have highlighted that nudging may be effective at producing immediate but rarely long-lasting behavioral changes.[ 16 , 20 ] In other health behavior domains, Li et al.[ 21 ] found a nonsignificant pooled effect of a nudge intervention on weight, BMI, and WC in a subgroup with follow-up exceeding 12 months. However, our findings may also be related to the small number of studies we included, with only one study that continued assessment beyond 1 month. Thus, additional original studies are needed to explore the long-term effects of nudge interventions. Moreover, the effect of nudge interventions was not significant in settings where vaccination of the population was widespread. These results suggest that for a complex issue such as vaccination challenges, the effect of nudging alone is limited. It has been demonstrated by several researchers that there are no separate methods and measures that can fully address VH and improve vaccination rates.[ 51 ] Although, combining traditional interventions with nudging interventions may exhibit unexpected effects, relevant scientific evidence remains limited. We also identified several nudging types based on existing frameworks, including approaches developed by scientists and policymakers, several of which showed beneficial results in changing COVID-19 vaccine uptake and vaccination intention. The most beneficial in terms of vaccine uptake was social norms and defaults, although those results were based on only two studies of 6,376[ 40 ] and 1,957[ 43 ] patients, while salient reminders also showed promising results, with most studies including this type of nudge reporting positive results (5 of 7).[ 25 , 35 , 37 , 40 , 44 ] Specifically, of these studies, nudges such as “Use familiar and trusted sources to provide vaccination reminders/recall” and “Description of vaccine retention for participants, highlighting vaccine ownership,” among others, increased favorable behaviors regarding COVID-19 vaccine. Additionally, salient reminders also had a positive impact on vaccination intentions. The review included many studies that assessed the impact of nudging on vaccination intentions; however, due to the different measures used in many studies to assess such intentions, and the risk of bias in approximating actual vaccination uptake via intentions,[ 52 ] we did not incorporate such data in quantitative analysis. This systematic evaluation has some advantages for policymakers and researchers, namely we have assembled a list of nudging strategies, including salient reminders, messengers, defaults, financial incentives, information frameworks, and social norms, each which has a different definition, is available to mitigate COVID-19 vaccine hesitancy, and is largely applicable to all types of vaccines. This study had several limitations. First, the vaccine uptake results exhibited high heterogeneity due to the small number of studies and the wide variation in specific implementation methods, outcome measures, and study settings. Second, the studies were conducted in middle- and high-income countries, where COVID-19 vaccine capacity and availability are relatively high[ 53 , 54 ]; this fact limits our interpretation of the study results. However, nudging interventions are generally less costly than many other large-scale health interventions[ 48 ]; thus, nudging interventions have particular potential in resource-limited settings or low-income countries. Third, most of the studies did not explicitly define the interventions as a nudge, and to capture as many publications on nudging as possible, we included additional keywords in the search terms, such as "behavioral strategy" and " behavioral control"; however, it remains possible that some relevant literature was missed. Finally, due to the number and heterogeneity of studies, we were unable to provide suggestions for combining types of nudge. Further exploration of nudges is needed, especially in the context of low-income countries, long-term interventions, and different types of nudge (alone or in combination). Conclusion Nudging may be a viable method to promote COVID-19 vaccination and reduce vaccine hesitancy, albeit of limited efficacy. Thus, nudges need to be used in combination with other intervention strategies. Most nudge strategies, such as social norms, defaults, and salient reminders, are recommended for consideration by public health practitioners and policymakers. However, further research is needed, especially in low-income countries and for long-term nudges. Declarations Acknowledgements None. Author Contributions JH and ZJR conceived and designed the study, ZJR conducted the literature search, extracted the data, assessed the quality of the study, performed statistical analysis and wrote the manuscript, JH and ZJR revised the manuscript, All authors read and approved the final manuscript. Funding This work was supported by Postgraduate Research and Practice Innovation Program of Jiangsu Province (KYCX21_0160) and Wuxi City Technology Development Fund(N20191007). Availability of Data and Materials All data generated or analyzed in this study is included in this published article and its additional information file. Ethics approval and consent to participate Not applicable. Consent for publication. Not applicable. Competing Interests The authors declare that they have none. Author information Department of Epidemiology and Health Statistics, Southeast University, Nanjing,210009,China Hui Jin, Jiarong Zhang References Edouard Mathieu, Hannah Ritchie LR-G, Appel C, Giattino C, Hasell J, Macdonald B. Saloni Dattani, Diana Beltekian, Esteban Ortiz-Ospina and Max Roser: Coronavirus Pandemic ( COVID - 19 ). Our World in Data 2020. Abu-Raddad LJ, Chemaitelly H, Ayoub HH, AlMukdad S, Yassine HM, Al-Khatib HA, Smatti MK, Tang P, Hasan MR, Coyle P, et al. Effect of mRNA Vaccine Boosters against SARS-CoV-2 Omicron Infection in Qatar. N Engl J Med. 2022;386(19):1804–16. Dubé E, MacDonald NE. COVID-19 vaccine hesitancy. Nat Rev Nephrol. 2022;18(7):409–10. MacDonald NE. Vaccine hesitancy: Definition, scope and determinants. Vaccine. 2015;33(34):4161–4. Bussink-Voorend D, Hautvast JLA, Vandeberg L, Visser O, Hulscher M. A systematic literature review to clarify the concept of vaccine hesitancy .Nat Hum Behav2022. Hou Z, Tong Y, Du F, Lu L, Zhao S, Yu K, Piatek SJ, Larson HJ, Lin L. Assessing COVID-19 Vaccine Hesitancy, Confidence, and Public Engagement: A Global Social Listening Study. J Med Internet Res. 2021;23(6):e27632. Sherman SM, Smith LE, Sim J, Amlôt R, Cutts M, Dasch H, Rubin GJ, Sevdalis N. COVID-19 vaccination intention in the UK: results from the COVID-19 vaccination acceptability study (CoVAccS), a nationally representative cross-sectional survey. Hum Vaccin Immunother. 2021;17(6):1612–21. 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Behavioural nudges increase COVID-19 vaccinations. Nature. 2021;597(7876):404–9. Rabb N, Swindal M, Glick D, Bowers J, Tomasulo A, Oyelami Z, Wilson KH, Yokum D. Evidence from a statewide vaccination RCT shows the limits of nudges. Nature. 2022;604(7904):E1–e7. Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, Shamseer L, Tetzlaff JM, Akl EA, Brennan SE. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. Syst reviews. 2021;10(1):1–11. Hausman DM, Welch B. Debate: To nudge or not to nudge. J Political Philos. 2010;18(1):123–36. Higgins J, Altman DG. Assessing risk of bias in included studies . 2008. Higgins JP, Green S. Cochrane handbook for systematic reviews of interventions . 2008. Dolan P, Hallsworth M, Halpern D, King D, Vlaev I. MINDSPACE : influencing behaviour for public policy . 2010. Sunstein CR. Nudging: A very short guide. Bus Econ. 2019;54(2):127–9. Motta M, Sylvester S, Callaghan T, Lunz-Trujillo K. Encouraging COVID-19 vaccine uptake through effective health communication .Frontiers in Political Science2021, 3 . Freeman D, Loe BS, Yu LM, Freeman J, Chadwick A, Vaccari C, Shanyinde M, Harris V, Waite F, Rosebrock L, et al. Effects of different types of written vaccination information on COVID-19 vaccine hesitancy in the UK (OCEANS-III): a single-blind, parallel-group, randomised controlled trial. Lancet Public Health. 2021;6(6):e416–27. Mehta SJ, Mallozzi C, Shaw PA, Reitz C, McDonald C, Vandertuyn M, Balachandran M, Kopinsky M, Sevinc C, Johnson A, et al. Effect of Text Messaging and Behavioral Interventions on COVID-19 Vaccination Uptake: A Randomized Clinical Trial. JAMA Netw Open. 2022;5(6):e2216649. Burger MN, Mayer M, Steimanis I. Repeated information of benefits reduces COVID-19 vaccination hesitancy: Experimental evidence from Germany. PLoS ONE. 2022;17(6):e0270666. Patel MS, Fogel R, Winegar AL, Horseman C, Ottenbacher A, Habash S, Dukes JL, Brinson TC, Price SC, Masoudi FA, et al. Effect of Text Message Reminders and Vaccine Reservations on Adherence to a Health System COVID-19 Vaccination Policy: A Randomized Clinical Trial. JAMA Netw Open. 2022;5(7):e2222116. Liu X, Zhao N, Li S, Zheng R. Opt-out policy and its improvements promote COVID-19 vaccinations. Soc Sci Med. 2022;307:115120. Ashworth M, Thunström L, Cherry TL, Newbold SC, Finnoff DC. Emphasize personal health benefits to boost COVID-19 vaccination rates .Proc Natl Acad Sci U S A2021, 118 (32). Santos HC, Goren A, Chabris CF, Meyer MN. Effect of Targeted Behavioral Science Messages on COVID-19 Vaccination Registration Among Employees of a Large Health System: A Randomized Trial. JAMA Netw Open. 2021;4(7):e2118702. Jensen UT, Ayers S, Koskan AM. Video-based messages to reduce COVID-19 vaccine hesitancy and nudge vaccination intentions. PLoS ONE. 2022;17(4):e0265736. Sasaki S, Saito T, Ohtake F. Nudges for COVID-19 voluntary vaccination: How to explain peer information? Soc Sci Med. 2022;292:114561. Tentori K, Pighin S, Giovanazzi G, Grignolio A, Timberlake B, Ferro A. Nudging COVID-19 Vaccine Uptake by Changing the Default: A Randomized Controlled Trial .Med Decis Making2022:272989x221101536. Campos-Mercade P, Meier AN, Schneider FH, Meier S, Pope D, Wengström E. Monetary incentives increase COVID-19 vaccinations. Science. 2021;374(6569):879–82. Gong Z, Tang Z, Li J. What Strategy Is Better for Promoting COVID-19 Vaccination? A Comparison Between Gain-Framed, Loss-Framed, and Altruistic Messages. Ann Behav Med. 2022;56(4):325–31. Bartoš V, Bauer M, Cahlíková J, Chytilová J. Communicating doctors' consensus persistently increases COVID-19 vaccinations .Nature2022. Reñosa MDC, Landicho J, Wachinger J, Dalglish SL, Bärnighausen K, Bärnighausen T, McMahon SA. Nudging toward vaccination: a systematic review .BMJ Glob Health2021, 6 (9). Benartzi S, Beshears J, Milkman KL, Sunstein CR, Thaler RH, Shankar M, Tucker-Ray W, Congdon WJ, Galing S. Should governments invest more in nudging? Psychological science2017, 28 (8):1041–1055. Reiter PL, McRee A-L, Pepper JK, Brewer NT. Default policies and parents’ consent for school-located HPV vaccination. J Behav Med. 2012;35(6):651–7. Attwell K, Freeman M. I Immunise: An evaluation of a values-based campaign to change attitudes and beliefs. Vaccine. 2015;33(46):6235–40. Omer SB, Salmon DA, Orenstein WA, deHart MP, Halsey N. Vaccine refusal, mandatory immunization, and the risks of vaccine-preventable diseases. N Engl J Med. 2009;360(19):1981–8. Sheeran P, Webb TL. The intention–behavior gap. Soc Pers Psychol Compass. 2016;10(9):503–18. Majid U, Ahmad M, Zain S, Akande A, Ikhlaq F. COVID-19 vaccine hesitancy and acceptance: a comprehensive scoping review of global literature .Health Promot Int2022, 37 (3). Louden EM. Scaling Up the Global COVID-19 Vaccination Program: Production, Allocation, and Distribution with an Emphasis on Equity. Yale J Biol Med. 2022;95(3):379–87. Supplementary Files Supplementary.pdf Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2430314","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":166398680,"identity":"0f57faeb-db3d-4e29-ab56-5ca94608be02","order_by":0,"name":"jiarong zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxUlEQVRIiWNgGAWjYBAC+wPnPz/4UGEjx8/eQKyegwfMDGecSTOW7DlArJbDBwykeVsOJxrMSCBSB2PbgQRj3obDCQaSjzfeYKixiSaohZnnwIGHc3ek55lLpxVbMBxLy20gpIVN4mCDwdsz1sWWs3PMJBgbDhPWwiP/mEGCt405ccPNM0RqkWA4xiDJ2+acuOEGD5FaDBjOsEEDGeiXBGL8AtTCDI3KwxtvfKixIawFRbtEAinKIVpI1TEKRsEoGAUjAwAAaZlFJWC3KAwAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-0759-1889","institution":"Southeast University","correspondingAuthor":true,"prefix":"","firstName":"jiarong","middleName":"","lastName":"zhang","suffix":""},{"id":166398681,"identity":"585944e3-89d4-4257-ba0e-2f8c43eb4d1c","order_by":1,"name":"Hui Jin","email":"","orcid":"https://orcid.org/0000-0003-0071-9755","institution":"Southeast University","correspondingAuthor":false,"prefix":"","firstName":"Hui","middleName":"","lastName":"Jin","suffix":""}],"badges":[],"createdAt":"2022-12-31 05:34:39","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2430314/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2430314/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":31479190,"identity":"18561ffd-d710-4ae8-842e-adcebcbf7828","added_by":"auto","created_at":"2023-01-12 13:31:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":43482,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of the selection process (PRISMA 2020)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-2430314/v1/9b49610d9e5dbc46d0b49643.png"},{"id":31479189,"identity":"05ef8dfb-57e2-4865-a99b-fb8b161e5c73","added_by":"auto","created_at":"2023-01-12 13:31:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":17252,"visible":true,"origin":"","legend":"\u003cp\u003eForest plot of the effect of nudge interventions on vaccine uptake\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-2430314/v1/dafb51599aa41b4234b82974.png"},{"id":31479188,"identity":"d573f234-6e92-416b-83c3-4eb74c5c5a76","added_by":"auto","created_at":"2023-01-12 13:31:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":21122,"visible":true,"origin":"","legend":"\u003cp\u003eMeta-regression plot of vaccination uptake over time\u003c/p\u003e","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-2430314/v1/521d8ed61bfc376ab699f614.png"},{"id":32423554,"identity":"100d3b81-b35a-4dbd-8051-504e523f7a57","added_by":"auto","created_at":"2023-02-03 08:51:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":846174,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2430314/v1/a622c155-adcb-4cd9-a34a-8b018262a10f.pdf"},{"id":31479191,"identity":"78f7b3cc-957e-4c66-afe5-d06f7502abb4","added_by":"auto","created_at":"2023-01-12 13:31:58","extension":"pdf","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":722847,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementary.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2430314/v1/b11b78ac1b691d9c099de85d.pdf"}],"financialInterests":"","formattedTitle":"Nudging vaccination against COVID-19: A systematic review and meta-analysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eVaccination is a key measure to control the ongoing COVID-19 pandemic. As of November 8, 2022, 68.2% of the world's population had received at least one dose of the COVID-19 vaccine, but vaccination rates vary widely between countries, with only 23.4% of people in low-income countries/areas receiving at least one dose.[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] Given the need for high vaccination rates to ensure adequate protection of populations and given the role of booster vaccination in combating the threat of new mutations,[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] there is a need to determine how to effectively increase uptake of COVID-19 vaccine; hence, understanding and addressing the concerns of people who are hesitant about vaccines is key to increasing vaccine intention and uptake.[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eVaccine hesitancy (VH) is defined as a \"Delay in acceptance or refusal of vaccination despite the availability of vaccination services.\u0026rdquo;[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] VH is complex and involves many issues, many of which are specific to the context of COVID-19.[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] For example, reports exist of a lack of confidence in the efficacy and/or safety of vaccines,[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] distrust of the health care system,[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] and widespread misinformation or rumors.[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] In low- and middle-income countries (LMICs), there are also environmental barriers, such as vaccine production and availability, and distance to vaccine sites.[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] A few interventions have been proposed and tested to address VH, including brief written educational interventions (e.g., pamphlets),[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] use of dialogue, communication, or informational tools.[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] Most interventions have focused on changing knowledge, attitudes, and behaviors related to vaccine information and/or safety to address vaccine hesitancy. Although some studies have reported statistically significant improvements in vaccination intention and uptake,[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] a 2017 literature review noted that many interventions designed to change individuals' perceptions and feelings about vaccination have shown limited effects.[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] In contrast to change, another range of intervention strategies focused on \u0026ldquo;nudging\u0026rdquo; or subtle changes to the design of the environment to encourage specific behaviors.[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] A nudge is an intervention strategy based on the dual-process model. Such interventions are usually easy to scale and implement at low cost.[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] Nudges primarily rely on System 1, which is fast, instinctive, and unconscious, rather than System 2, which is slow and conscious.[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] This strategy has been shown to be effective in diet change and weight loss[\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] chronic disease self-management[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], for example. Regarding vaccination, a field trial showed that text messaging \"nudges\" encouraged people to receive vaccination against COVID-19.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] However, another trial that evaluated the effectiveness of text nudges sent by the Rhode Island Department of Health showed that none of the nudges were effective in boosting vaccination rates for COVID-19.[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eTo date, the effectiveness of nudging interventions is unclear with respect to intentions and behaviors related to COVID-19 vaccination. Therefore, we synthesized the available evidence on the use of nudge techniques in increasing intentions and behaviors associated with the COVID-19 vaccine. The purpose of this review was to assess whether nudge interventions used to improve COVID-19 VH are effective and to provide empirical evidence for researchers and policymakers worldwide.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSearch strategies\u003c/h2\u003e \u003cp\u003eThis systematic review was developed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Statement 2020 (PRISMA)[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] We have registered an agreement for this review with PROSPERO (registration number: CRD42022381558). A literature search was conducted of PubMed, Web of Science, and Scopus (end-of-search date: August 5, 2022).\u003c/p\u003e \u003cp\u003eWe included the Medical Subject Headings (MeSH): \u0026ldquo;behavioral control,\u0026rdquo; \u0026ldquo;vaccination,\u0026rdquo; \u0026ldquo;vaccines,\u0026rdquo; \u0026ldquo;vaccination coverage,\u0026rdquo; \u0026ldquo;SARS-CoV-2,\u0026rdquo; and \u0026ldquo;COVID-19,\u0026rdquo; and the following non-MeSH terms: \u0026ldquo;behavioral intervention,\u0026rdquo; \u0026ldquo;behavioral strategy,\u0026rdquo; \u0026ldquo;nudge,\u0026rdquo; \u0026ldquo;nudging,\u0026rdquo; and \u0026ldquo;immunization rates\u0026rdquo; using Boolean operators \u0026ldquo;AND\u0026rdquo; and \u0026ldquo;OR\u0026rdquo; to combine keywords into the final search string (Supplementary Table S1). We scanned a list of references from relevant systematic reviews to identify randomized controlled trials that met our inclusion criteria.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEligibility Criteria\u003c/h3\u003e\n\u003cp\u003eGiven that people of all ages can be vaccinated, we are not imposing any restrictions at the population level. Thaler and Sunstein[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] defined a nudge as \u0026ldquo;any addition to or modification of the environment that influenced consumers in a predictable way, without changing economic incentive;\u0026rdquo; however, this definition is difficult to implement. Hausman and Welch added more detail to this definition by emphasizing that a \u0026ldquo;nudge\u0026rdquo; represents an attempt to prevent irrational choices by actively changing behavioral biases.[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] We used this definition to exclude interventions that were not consistent with nudge strategies. The eligibility criteria are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eInclusion and exclusion criteria.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCriterion\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInclusion\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eExclusion\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePopulation and sample\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eGeneral population, reflecting all vaccination target groups and all stakeholders involved in vaccination decisions\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLiterature focus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1. Full-text papers and reports, peer reviewed articles.\u003c/p\u003e \u003cp\u003e2. Interventions belonged to the nudge category\u003c/p\u003e \u003cp\u003e3. The results were the impact of nudging on COVID-19 vaccine uptake and/or vaccination intention\u003c/p\u003e \u003cp\u003e4. The study design was a RCT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1. Articles that are abstract only and/or lack retrievable full text\u003c/p\u003e \u003cp\u003e2. Literature reviews, editorial letters and comments, theoretical/background papers\u003c/p\u003e \u003cp\u003e3. Interventions not attributed to a nudge strategy\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003elangue\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eEnglish\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eStudy Selection, Data Extraction, And Quality Assessment\u003c/h3\u003e\n\u003cp\u003eThe following information was extracted and validated for the included studies using a standardized Excel form: Study and participant characteristics (e.g., authors, publication date, country, sample size, and population description), intervention characteristics (study group, control group description, intervention strategies, time points), and study outcomes (vaccination uptake, intention to vaccinate). If the outcome of a study was measured at multiple time points, we selected the outcome that the study authors specified as the primary outcome; if this was unclear, we averaged the results over time. For multi-arm studies, data from each arm with different nudging elements were extracted.\u003c/p\u003e \u003cp\u003eWe assessed the risk of bias of the included studies using the Cochrane Risk of bias tool.[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] For each study, each criterion was scored as low risk, unclear risk, or high risk of bias.\u003c/p\u003e\n\u003ch3\u003eData Synthesis And Analysis\u003c/h3\u003e\n\u003cp\u003eRisk ratios (RRs) and 95% confidence intervals (CIs) were used to calculate the pooled effect size. We considered the different nudging interventions in each study and combined data using a random-effects meta‐analysis of the number of people receiving immunizations. When summary statistics were not provided, we calculated RRs based on the number of events and individuals in each intervention group. Conversely, if the total number of events was missing, we estimated values using the summary statistics and their confidence intervals. Publication bias was evaluated using funnel plots, and Egger's test and Begg's test were used to evaluate the asymmetry of funnel plots. Significant publication bias was considered present if p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eSensitivity analysis was conducted to assess the stability of the study using the leave-one method Subgroup analysis was performed at different time points to evaluate the outcomes (\u0026lt;\u0026thinsp;4 or \u0026ge;\u0026thinsp;4 weeks), comparison (no intervention/usual care or other intervention), study location (US or Europe), year (2021 or 2022) the proportion of persons vaccinated (\u0026ge;\u0026thinsp;70% or༜70%) and types of nudge. Nudging interventions were summarized drawing on the MINDSPACE framework (Defaults, Salience, Messenger, Incentives, Ego, Priming, Commitment, Affect, and Norms) and Sunstein's list (default rules, simplification, increases in ease and convenience, uses of social norms, warnings, disclosure, pre-commitment strategies, reminders, Elicits the intention to act and informs people of the nature and consequences of their past choices).[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] We performed a meta-regression to assess the validity of the hypothesis that RR reduction was proportional to the intervention\u0026rsquo;s time-lapse. All statistical analyses were performed via R 3.6.2.\u003c/p\u003e \u003cp\u003eBeyond vaccination uptake, conducted a narrative synthesis of other outcomes related to vaccination (vaccination intention).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe search identified 2,596 articles ranging from January 1st, 2020, to August 5\u003csup\u003eth,\u003c/sup\u003e 2022 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), of which 15 peer-reviewed articles were included in the final analysis (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of the included randomized controlled trials (RCTs).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAuthor (Year)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eParticipants\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCountry\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eArm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eInterventions\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eComparison\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTime points\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eoutcome\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDai(2021)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;93354\u003c/p\u003e \u003cp\u003e(patients registered at UCLA health)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBasic reminder/Ownership reminder\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNo text message\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eVaccination uptake (+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBartoš(2022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;2101(general population adults)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCzekh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eConsensus condition\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNo information\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2 weeks/4 months\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate (+) and Vaccination uptake(+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSasaki(2022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;1595(25\u0026ndash;34 young and 65\u0026ndash;74 elderly)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eJapan\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003esocial-comparison/gain-framed social influence/loss-framed social influence\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBasic Information\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate(0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTentori(2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;2000(50\u0026ndash;59 adults)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eItaly\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eopt-out group\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eOPT-IN group\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eVaccination uptake (+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCampos(2021)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;8286(18\u0026ndash;49 adults)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSweden\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIncentives/Social impact/Information/Arguments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBasic reminder\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention /4 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate (0) and Vaccination uptake (0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSantos(2021) \u0026dagger;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;9723(Employees registered at Geisinger Health System)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003esocial norms/reframing risks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDelayed control\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eVaccination registration (+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAshworth(2021)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;3048(general population)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePrivate benefit/ Social benefit/ Economic benefit/Vaccine safety\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNo information\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate (+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMehta(2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;16045(patients visit at a Penn Medicine primary care provider)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u0026times; 4 design; Call Back/ In-Bound Call\u0026thinsp;+\u0026thinsp;Standard Msg/ Clinician Endorsement/ Scarcity/ Opt-Out Framing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eoutbound call only\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1 month\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eVaccination uptake (-)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePatel(2022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;2000(Ascension Associate Employee.)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eText message\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eUsual care\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eVaccination uptake (+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eJensen(2022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;890(general population adults)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVideo-based messages: safety/ social norm/ response efficacy/ self-efficacy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBasic Information\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate(+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLiu(2022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;1926(general population)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChina\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eConventional Opt-out/ Improved Opt-out\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eOPT-IN group\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate(0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMotta(2021)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;7064(general population adults)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3 \u0026times; 2 \u0026times; 2 design; personal health risks/collective public health consequences of not vaccinating/ economic costs\u0026thinsp;+\u0026thinsp;lay source/ expert sources\u0026thinsp;+\u0026thinsp;Highlighting the rigors of clinical trials/ Not highlighting the rigor of clinical trials\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNo information\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate(0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFreeman(2021)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;16455(general population adults)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUK\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecollective benefit (3 conditions)/personal benefit/seriousness/safety, direct/safety, indirect/collective and personal benefit/full combination\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSafety and effectiveness statement\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate (0)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBurger(2022)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;1324(general population)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGermany\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDebunking/ Benefits/ Facilitation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNo information\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate (-)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGong(2021)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;1316(general population adults)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChina\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGain-Framed/ Loss-Framed/ Altruistic Messages\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNo information\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAfter intervention\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eIntention to vaccinate (+)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003e* The sign in parentheses indicates whether the results supported the effectiveness of the respective intervention (+), provided evidence of lack of effectiveness (\u0026minus;), or reported mixed results (0).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003e\u0026dagger; The primary outcome of the study was vaccination registration, but given that the study population was employees of a large health system and that there were employee-only vaccination clinics with approximate vaccination registration and actual vaccination numbers, we treated the outcome as vaccine uptake.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eA total of 167,127 people were included, predominately from the general adult population. Most of the included studies continued for 1 month after the intervention,[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan additionalcitationids=\"CR34 CR35 CR36 CR37 CR38 CR39 CR40 CR41 CR42 CR43 CR44\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] except one study, which continued for 4 months.[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] All studies were conducted in high-income or upper middle-income countries (USA (n\u0026thinsp;=\u0026thinsp;7),[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan additionalcitationids=\"CR40\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] China (n\u0026thinsp;=\u0026thinsp;2),[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] Czech Republic (n\u0026thinsp;=\u0026thinsp;1),[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] Italy (n\u0026thinsp;=\u0026thinsp;1),[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] Sweden (n\u0026thinsp;=\u0026thinsp;1)[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], Japan (n\u0026thinsp;=\u0026thinsp;1),[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] UK (n\u0026thinsp;=\u0026thinsp;1),[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] and Germany (n\u0026thinsp;=\u0026thinsp;1).[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] Seven studies incorporated control groups that received no intervention or usual care.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eThe risk of bias for all included studies is summarized in Supplementary Fig.\u0026nbsp;1. Full details of the risk of bias assessment for each study are provided in Supplementary Table S2. Of the 15 randomized controlled trials included in the evaluation, 10 were rated as of high quality and none as of low quality. A lack of allocation concealment description and clear blinding were common factors that limited the quality of the studies.\u003c/p\u003e\n\u003ch3\u003eCharacteristics Of Nudge Interventions\u003c/h3\u003e\n\u003cp\u003eAfter considering the operability of nudge strategies in the intervention studies, we identified a total of six types of nudging interventions employed across the selected studies (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Almost all of the included studies (12 of 15) were multinudge element interventions[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan additionalcitationids=\"CR34 CR35\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan additionalcitationids=\"CR39 CR40 CR41\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]; nine studies applied the nudge intervention of a salient reminder,[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan additionalcitationids=\"CR35 CR36\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan additionalcitationids=\"CR40\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] seven studies applied an information framework,[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] three studies applied messaging,[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] three studies applied social norms,[\u003cspan additionalcitationids=\"CR41\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] two studies applied defaults,[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] and one study applied financial incentives.[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of nudging interventions.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eType of nudging\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRationale\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNudging-based approaches employed in the included studies\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSalient reminder\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eA reminder can ensure that people can act immediately on the salient information that is provided in that particular moment.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1. Use familiar and trusted sources (e.g., health centers, large survey companies, etc.) to provide vaccination reminders/recalls;[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e2. Write down arguments that could best convince another person to get vaccinated;[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e3. Highlighting the safety and efficacy of COVID-19 vaccine;[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e4. Juxtaposing the risk of the vaccine with the risk of COVID-19;[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e5. Highlighting the safety and rigor of COVID-19 vaccine clinical trials;[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e6. SMS highlights the limited availability of vaccines;[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e7. Description of vaccine retention for participants, highlighting vaccine ownership;[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e8. Video-based reminders and recalls to highlight vaccine safety, efficacy or vaccination retention information, convenience, etc;[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e9. Receiving information debunking vaccination myths increases the intention to get vaccinated.[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFinancial Incentives\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIncentives, both tangible and intangible, can increase favoured behaviour.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1. Provide monetary incentives to increase vaccination intentions and actual uptake.[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMessenger\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChanging the source from which the information is delivered (eg, a trusted peer or a doctor) can alter the level of emphasis on the information.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1. Provide the true view held by physicians to correct misunderstandings about vaccine uptake);[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e2. Clinicians provide vaccination advice;[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e3. Expert (vs. lay) sources of vaccine support information.[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInformation Framework\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThe same outcome is perceived differently when the benefits gained (eg, lives saved) and losses avoided (eg, deaths avoided) inform the message.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1. Gain-framed messaging (describing benefits of receiving vaccines)[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] versus loss-framed messaging (describing the cost of not receiving the vaccine);[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e2. Make a list who would benefit from the participant getting vaccinated;[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e3. Describe the private[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], social[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], and economic benefit[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] of vaccination;\u003c/p\u003e \u003cp\u003e4. Describe the personal[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], Economic[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], and Collective[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] Health Risk Frames);\u003c/p\u003e \u003cp\u003e5. Altruistic messages to motivate people to accept COVID-19 vaccination.[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSocial Norms\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePeople tend to behave in ways that are consistent with their perceptions of the social environment and widely accepted behaviors in their peer groups.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1. Based on emails, videos, etc. indicating that a large proportion of people around or colleagues have chosen to be vaccinated to improve vaccine uptake).[\u003cspan additionalcitationids=\"CR41\" citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDefaults\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChanging whether something is the default option versus requiring explicit opt-in can change behaviour.[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1. Vaccination appointment has been scheduled (with opting out possible);[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e2. Opt-out policy and its improvements(different information was provided for the opt-out policy).[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eEffects Of Nudging Interventions\u003c/h3\u003e\n\u003cp\u003eVarious outcome measures were used to assess the effect of nudging interventions. The most frequent were vaccination uptake (n\u0026thinsp;=\u0026thinsp;7)[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] and intention to vaccinate (n\u0026thinsp;=\u0026thinsp;10).[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] As can be seen from Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, half of the articles reported positive effects (n\u0026thinsp;=\u0026thinsp;7),[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] while other articles reported partially positive effects with mixed or inconclusive overall results (n\u0026thinsp;=\u0026thinsp;6).[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] Significantly, two articles identified that nudging interventions has no effect.[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] These negative findings involved nudges that were divided into different texts plus inbound/outbound call groups[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] and a message intervention debunking vaccination myths or highlighting benefits.[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] Detailed characteristics of all nudge interventions are described in Supplementary Table S2.\u003c/p\u003e\n\u003ch3\u003eImpact Of Nudge Interventions On Vaccine Uptake\u003c/h3\u003e\n\u003cp\u003eSeven studies reported vaccine uptake results, with a total of 131,719 people included.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] Five studies found statistically significant increases in vaccination uptake compared with control groups,[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] one study[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] reported mixed results, and one study[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] identified no effects from the nudging intervention. The pooled results showed that vaccine uptake was significantly higher in the nudging intervention group compared to the control (RR: 1.19, 95% CI [1.07, 1.33], p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The heterogeneity was 93%, and a random-effects model was adopted. The funnel plot appeared to be asymmetric (Supplementary Figure S2), but Begg's test (p\u0026thinsp;=\u0026thinsp;0.195) and Egger's test (p\u0026thinsp;=\u0026thinsp;0.590) revealed no major publication bias in the included articles. Sensitivity analyses using the leave-one-out method did not significantly alter the overall outcome of vaccine uptake (Supplementary Figure S3\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results of the subgroup analysis are shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Supplementary Figures S4\u0026ndash;S9. The nudging intervention appeared to have a greater effect on vaccine uptake in the group with follow-up \u0026lt;\u0026thinsp;4 weeks (RR: 1.59, 95% CI [1.16, 2.19]) than in the group with follow-up \u0026ge;\u0026thinsp;4 weeks (RR: 1.12, 95% CI [1.05, 1.20]), although the difference was not significant. When we stratified, by comparison, the difference in vaccine uptake between the trial and control groups was significant only when the control was no intervention/usual care. Nudging appeared to have a more pronounced effect on vaccine uptake when the COVID-19 vaccine was available early and when general vaccination rates were low (i.e., literature published in 2021 or when the control group had vaccination rates less than 70%). Regardless of whether the study was conducted in the United States or Europe, the boost to vaccination uptake was significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). There was no strong evidence that the information framework was effective at increasing vaccine uptake rates (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). All types of nudge interventions except the information framework had a weak positive effect on vaccine uptake (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Among the six nudge types, a stronger effect on vaccine update was observed for social norms (RR: 2.04, 95% Cl [1.61, 2.57]), defaults (RR: 1.32, 95% Cl [1.03, 1.69]), and salient reminders (RR: 1.19, 95% Cl [1.04, 1.36]).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSubgroup analysis of nudging intervention on vaccine uptake.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntervention type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eOutcome: received immunizations\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eIllustrative comparative risks* (95% CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eRelative effect (95% CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eNo of participants (studies)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAssumed risk\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCorresponding risk\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eWithout intervention\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eWith intervention\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNudge(summary)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e203 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e242 per 1000\u003c/p\u003e \u003cp\u003e(217 to 270)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.19(1.07 to 1.33)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e131,719(7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTime points\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNudge(\u0026ge;\u0026thinsp;4 weeks)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e215 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e241 per 1000\u003c/p\u003e \u003cp\u003e(226 to 258)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.12(1.05 to 1.20)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e118,196(4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNudge(\u0026lt;\u0026thinsp;4 weeks)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e74 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e118 per 1000\u003c/p\u003e \u003cp\u003e(86 to 162)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.59(1.16 to 2.19)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13,523(3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ecomparsion\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNo intervention/usual care\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e147 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e179 per 1000\u003c/p\u003e \u003cp\u003e(168 to 191)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.22(1.14 to 1.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e96,974(3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eOther intervention\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e415 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e486 per 1000\u003c/p\u003e \u003cp\u003e(398 to 593)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.17(0.96 to 1.43)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e34,745(4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eStudy location\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eUS\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e131 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e168 per 1000\u003c/p\u003e \u003cp\u003e(140 to 199)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.28(1.07 to 1.52)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e120,965(4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eEurope\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e668 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e695 per 1000\u003c/p\u003e \u003cp\u003e(681 to 708)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.04(1.02 to 1.06)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10754(3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eYear\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e2021\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e201 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e255 per 1000\u003c/p\u003e \u003cp\u003e(219 to 297)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.27(1.09 to 1.48)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e90086(3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e2022\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e239 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e258 per 1000\u003c/p\u003e \u003cp\u003e(246 to 272)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.08(1.03 to 1.14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21622(4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eProportion of Vaccination\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e\u0026ge;\u0026thinsp;70%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e715 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e744 per 1000\u003c/p\u003e \u003cp\u003e(729 to 758)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.04(1.02 to 1.06)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8797(2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e༜70%\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e131 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e169 per 1000\u003c/p\u003e \u003cp\u003e(144 to 197)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.29(1.10 to 1.50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e122922(5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNudge types\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSalient reminder\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e173 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e206 per 1000\u003c/p\u003e \u003cp\u003e(180 to 235)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.19(1.04 to 1.36)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e118779(5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMessenger\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e485 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e519 per 1000\u003c/p\u003e \u003cp\u003e(485 to 548)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.07(1.00 to 1.13)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5930(2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDefaults\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e99 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e131 per 1000\u003c/p\u003e \u003cp\u003e(102 to 167)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.32(1.03 to 1.69)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1957(1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFinancial incentives\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e716 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e759 per 1000\u003c/p\u003e \u003cp\u003e(723 to 788)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.06(1.01 to 1.10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3909(1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eInformation Framework\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e716 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e737 per 1000\u003c/p\u003e \u003cp\u003e(709 to 766)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 1.03(0.99 to 1.07)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3892(1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSocial Norms\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32 per 1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65 per 1000\u003c/p\u003e \u003cp\u003e(52 to 82)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRR 2.04(1.61 to 2.57)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6376(1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eMeta-regression analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) indicated a nonsignificant association between vaccination and passage of time within 4 months (p\u0026thinsp;=\u0026thinsp;0.095), but only one study exceeded 1 month; therefore, we excluded this study to explore a 1-month trend. The results after exclusion showed that within 1 month, the increase in vaccination was inversely associated with the passage of time (p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eImpact Of Nudge Interventions On Vaccine Intention\u003c/h3\u003e\n\u003cp\u003eAmong the 10 studies that considered intention to vaccinate as the primary outcome of interest,[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] three studies found statistically significant increases in vaccination intention compared with control groups.[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] More than half of the studies (6 of 10) reported mixed results regarding vaccination intention among study participants,[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] and one study identified no effects of the nudging intervention on vaccination intention (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e summarizes the characteristics of the vaccine intentions for outcome studies. The supplementary table S2 provides a more detailed view of each study.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of nudge interventions on vaccination intentions.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTypes of nudging\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eImplementation details\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFindings\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBartoš et al[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMessenger\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eConsensus condition, participants were provided with a summary of the survey among medical doctors, including three charts that displayed the distribution of doctors\u0026rsquo; responses regarding their trust in the vaccines, willingness to get vaccinated themselves and intentions to recommend the vaccine to patients\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePublic misconceptions about what doctors think about COVID-19 vaccines are common, and correcting them will boost vaccination intentions.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSasaki et al[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInformation Framework/ Social Norms\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eThe three groups were randomly assigned peer information: comparison, influence-gain, and influence-loss. The effect of each piece of information on vaccination intentions was compared\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eThe influence gain nudge was effective in increasing the number of older adults who newly decided to vaccinate, but had no boost for younger adults who were less willing to vaccinate at baseline.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCampos et al[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFinancial Incentives/ Salient reminder/Information Framework\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eThe effect of a small cash reward, around US \u003cspan\u003e$\u003c/span\u003e24, was compared with the effect of several behavioral nudges. The nudge measures are social impact condition, arguments condition and information condition\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFinancial incentives significantly increased vaccination intentions and coverage rates, while other incentives increased vaccination intentions but had little effect on vaccination rates\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAshworth et al[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInformation Framework/ Salient reminder\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\"Private benefit\", \"social benefit\", \"economic benefit\" and \"vaccine safety\" information individually and in combination to examine the impact on vaccine intent, Participants were randomly assigned to one of nine informational treatments\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSeveral forms of public information can increase vaccine intent, but messages that emphasize individual health benefits have the greatest impact.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eJensen et al[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSalient reminder/ Social Norms\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFour different treatment videos were made based on planned behavior theory, (i) attitudes about vaccine safety, (ii) normative beliefs about subjective social norms of vaccination, (iii) attitudes about vaccine efficacy (response effect), and (iv) perceived behavioral control over vaccination (self-efficacy).\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eShort video encouraging messages that address specific issues with COVID-19 vaccines increase vaccination intentions\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLiu et al[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDefaults\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eThere are seven vaccination policies, including an opt-in policy with no default, an opt-out policy with vaccination as the default, and five improved versions of the latter, including Social Norm, Transparency, Education, Feedback and Opportunity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOpt-out policies and their improvements (with the exception of opt-out transparency) increase the willingness to vaccinate.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMotta et al[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInformation Framework/Messenger\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRespondents were randomly assigned to read a short pro-vaccine opinion article, depending on (i) the framework (individual health risks, collective public health consequences and economic costs of not vaccinating), (ii) the source of information (i.e. lay versus expert sources), And (iii)the presence or absence of pre-bunking information highlighting the rigors of clinical trials prior to reading the opinion piece.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRegardless of the source, information that emphasizes the individual health risks and collective health consequences of not vaccinating can significantly increase Americans' intention to get vaccinated. The economic cost framework had no significant effect on vaccine intent\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFreeman et al[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInformation Framework/ Salient reminder\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eParticipants were randomly assigned to ten information conditions stratified by their level of vaccine acceptance (willingness, skepticism, or strong hesitation). Condition 1 was the control group, whose text included safety and efficacy claims taken from the NHS website. Three conditions address only collective interests (conditions 2, 3 and 4), one individual interests only (condition 5), one combines collective and individual interests (condition 9), one concerns the severity of the pandemic (condition 6), two concerns security issues (conditions 7 and 8), and the final condition addresses the complete combination of interests, Seriousness and safety issues (Condition 10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIn populations that are very hesitant about COVID-19 vaccines, the provision of information of individual benefit reduced indecision to a greater extent than information of collective benefit.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBurger et al[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSalient reminder/Information Framework\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAssess whether debunking vaccination myths, highlighting the benefits of vaccination, or sending vaccination reminders will reduce hesitation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo increase in the willingness to vaccinate, regardless of the information provided\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGong et al[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eInformation Framework\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAn online survey experiment consisting of a control group (exposed to non-framing information) and three experimental groups (exposed to gain framing, loss framing, or altruistic information) was designed to assess vaccination intentions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePeople exposed to the gain frame, loss frame, or altruistic messages were more likely to be vaccinated against COVID-19 than those exposed to non-frame messages. In addition, the loss of frame information had a more significant effect on vaccination intentions than the other two types of information.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThere was mixed evidence regarding the effectiveness of nudging for increasing vaccination intentions for different information frames. A randomized controlled trial in Japan[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] evaluated the effect of different peer messages on vaccination intentions; only gaining frame messages were effective at increasing the number of older adults who newly decided to get vaccinated. In contrast, a study in China showed[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] that people exposed to lose frames showed higher intentions of obtaining a COVID-19 vaccine compared to gain frame messages. Ashworth et al.[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] defined three messages emphasizing different benefits of the vaccine and one emphasizing vaccine safety, and evaluated the impact on vaccine intentions of transmitting the four messages individually and in combination. The results suggested that although safety concerns were the main reason for hesitation regarding the COVID-19 vaccine, the group exposed to the vaccine safety message did not exhibit significantly increased vaccination intentions.\u003c/p\u003e \u003cp\u003eThe message emphasizing personal health benefits had the greatest impact. An RCT[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] conducted in the United States prior to the introduction of the COVID-19 vaccine found that intention to receive COVID-19 vaccination increased significantly when information was tailored to individual health risks, the consequences of not receiving the vaccine, and when these framing messages came from medical experts. In the United Kingdom, a randomized controlled trial[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] similarly showed that individuals who were strongly hesitant about the COVID-19 vaccine were influenced more effectively by personal benefit messages than were those who received collective benefit messages.\u003c/p\u003e \u003cp\u003eIn addition to information frames, other types of nudges also led to different results. A study in the Czech Republic[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] focused of a facilitation intervention on changing the messengers assigned to convey vaccine-related health messages. A study in the US[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] adopted a short video of c. 30 seconds for the specific problem of COVID-19 vaccine, Campos et al.[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] used incentives as a mechanism for behavior change. In each of these studies, nudge measures all increased vaccination intention to varying degrees, but it is worth noting that in Campos et al., salient reminders and information framework nudge measures increased intention to vaccinate but had a small and statistically insignificant effect on vaccination rates. Mixed results were also seen in a randomized trial in China,[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] in which investigators considered the use of defaults and refined defaults in the unvaccinated population to increase intention to receive the COVID-19 vaccination. Opt-out policies increased the intention to receive vaccination, but none of the refined versions resulted in significant changes in participants' intention to vaccinate compared to the traditional opt-out condition. A German registry trial showed[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] that willingness to vaccinate did not increase regardless of whether the information provided debunked vaccination myths or emphasized the benefits of vaccination or sent vaccination reminders.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis systematic review is the only synthesis of available evidence on how nudging affects intentions and behaviors related to COVID-19 vaccine uptake. Overall, data from seven randomized controlled trials were pooled to show that the nudge strategy slightly increased COVID-19 vaccine uptake (RR: 1.19, 95% Cl [1.07, 1.33]). These increases were more pronounced in the short-term (\u0026lt;\u0026thinsp;4 weeks), with a no intervention/usual care control group, in the US, when vaccine the vaccine had recently become available (year\u0026thinsp;=\u0026thinsp;2021 and proportion of the vaccinated population vaccinated\u0026thinsp;\u0026lt;\u0026thinsp;70%), and for the nudging type of social norms. Nine of the ten studies involving vaccination intention outcomes reported positive or partially positive results. These findings indicated that low-cost and short-duration nudges may be an effective way to mitigate COVID-19 vaccine hesitancy.\u003c/p\u003e \u003cp\u003eA previous systematic review found that nudging interventions showed the potential to increase vaccine confidence and uptake [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]; this is consistent with our results. Although our study showed that nudging measures can only foster small improvements in vaccination update, given the generally easy and low-cost implementation of nudges,[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] they represent a practical approach that can be applied to large populations. Available evidence suggests that even small gains, when applied to large populations, can represent the vaccination of millions of people.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] In the studies included in the present review, some control groups also received interventions; for example, some studies used basic information or simple reminders with the control group.[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] In our analysis, by comparing no-intervention control groups with control groups that received other interventions, the pooled results suggested that adding targeted nudges to existing interventions may be an important consideration to improve vaccine behavior and intentions. In addition, there were differently worded interventions in the included multi-arm studies. In a study of more than 90,000 people in California,[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] researchers found that \u0026ldquo;ownership\u0026rdquo; reminders boosted vaccination rates by approximately 1.1 percentage points more than did basal reminders. However, in Liu et al.,[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] none of the improved versions resulted in a significant change in participants' willingness to receive vaccination compared to the traditional opt-out condition. Some studies also suggested that using a nudge intervention with groups that already have ambivalent feelings about vaccination may be counterproductive.[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] Therefore, subtle changes, including in wording based on original nudges, require careful design and further study.\u003c/p\u003e \u003cp\u003eA key finding of our analysis was that the effect of the nudging intervention on COVID-19 vaccine uptake gradually decreased over time, and the results presented in the follow-up time point subgroup appeared to corroborate such findings. Some studies have highlighted that nudging may be effective at producing immediate but rarely long-lasting behavioral changes.[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] In other health behavior domains, Li et al.[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] found a nonsignificant pooled effect of a nudge intervention on weight, BMI, and WC in a subgroup with follow-up exceeding 12 months. However, our findings may also be related to the small number of studies we included, with only one study that continued assessment beyond 1 month. Thus, additional original studies are needed to explore the long-term effects of nudge interventions. Moreover, the effect of nudge interventions was not significant in settings where vaccination of the population was widespread. These results suggest that for a complex issue such as vaccination challenges, the effect of nudging alone is limited. It has been demonstrated by several researchers that there are no separate methods and measures that can fully address VH and improve vaccination rates.[\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] Although, combining traditional interventions with nudging interventions may exhibit unexpected effects, relevant scientific evidence remains limited.\u003c/p\u003e \u003cp\u003eWe also identified several nudging types based on existing frameworks, including approaches developed by scientists and policymakers, several of which showed beneficial results in changing COVID-19 vaccine uptake and vaccination intention. The most beneficial in terms of vaccine uptake was social norms and defaults, although those results were based on only two studies of 6,376[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] and 1,957[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] patients, while salient reminders also showed promising results, with most studies including this type of nudge reporting positive results (5 of 7).[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] Specifically, of these studies, nudges such as \u0026ldquo;Use familiar and trusted sources to provide vaccination reminders/recall\u0026rdquo; and \u0026ldquo;Description of vaccine retention for participants, highlighting vaccine ownership,\u0026rdquo; among others, increased favorable behaviors regarding COVID-19 vaccine. Additionally, salient reminders also had a positive impact on vaccination intentions. The review included many studies that assessed the impact of nudging on vaccination intentions; however, due to the different measures used in many studies to assess such intentions, and the risk of bias in approximating actual vaccination uptake via intentions,[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e] we did not incorporate such data in quantitative analysis.\u003c/p\u003e \u003cp\u003eThis systematic evaluation has some advantages for policymakers and researchers, namely we have assembled a list of nudging strategies, including salient reminders, messengers, defaults, financial incentives, information frameworks, and social norms, each which has a different definition, is available to mitigate COVID-19 vaccine hesitancy, and is largely applicable to all types of vaccines.\u003c/p\u003e \u003cp\u003eThis study had several limitations. First, the vaccine uptake results exhibited high heterogeneity due to the small number of studies and the wide variation in specific implementation methods, outcome measures, and study settings. Second, the studies were conducted in middle- and high-income countries, where COVID-19 vaccine capacity and availability are relatively high[\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]; this fact limits our interpretation of the study results. However, nudging interventions are generally less costly than many other large-scale health interventions[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]; thus, nudging interventions have particular potential in resource-limited settings or low-income countries. Third, most of the studies did not explicitly define the interventions as a nudge, and to capture as many publications on nudging as possible, we included additional keywords in the search terms, such as \"behavioral strategy\" and \" behavioral control\"; however, it remains possible that some relevant literature was missed. Finally, due to the number and heterogeneity of studies, we were unable to provide suggestions for combining types of nudge. Further exploration of nudges is needed, especially in the context of low-income countries, long-term interventions, and different types of nudge (alone or in combination).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eNudging may be a viable method to promote COVID-19 vaccination and reduce vaccine hesitancy, albeit of limited efficacy. Thus, nudges need to be used in combination with other intervention strategies. Most nudge strategies, such as social norms, defaults, and salient reminders, are recommended for consideration by public health practitioners and policymakers. However, further research is needed, especially in low-income countries and for long-term nudges.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJH and ZJR conceived and designed the study, ZJR conducted the literature search, extracted the data, assessed the quality of the study, performed statistical analysis and wrote the manuscript, JH and ZJR revised the manuscript, All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Postgraduate Research and Practice Innovation Program of Jiangsu Province (KYCX21_0160) and Wuxi City Technology Development Fund(N20191007).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of Data and Materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analyzed in this study is included in this published article and its additional information file.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have none.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDepartment of Epidemiology and Health Statistics,\u0026nbsp;Southeast University, Nanjing,210009,China\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHui Jin, Jiarong Zhang\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eEdouard Mathieu, Hannah Ritchie LR-G, Appel C, Giattino C, Hasell J, Macdonald B. 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Yale J Biol Med. 2022;95(3):379\u0026ndash;87.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Nudge, Vaccination, COVID-19, Systematic review","lastPublishedDoi":"10.21203/rs.3.rs-2430314/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2430314/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e New approaches to mitigate vaccine hesitancy (VH) and improve vaccine uptake and willingness are urgently needed. Nudging is a new approach that has shown effective results in several areas of health. However, the effectiveness is unclear regarding nudging interventions to improve intentions and behaviors related to COVID-19 vaccination.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods: \u003c/strong\u003eWe searched PubMed, Web of Science, and Scopus until August 5, 2022. Randomized controlled trials (RCTs) were considered to determine whether nudging improved COVID-19 vaccination behavior and intent. The risk ratio (RR) and 95% confidence interval (CI) were used as pooled measures to assess vaccination behavior. Intention to vaccinate was reported in the narrative synthesis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults:\u003c/strong\u003e A total of 15 RCTs involving 167,127 individuals were included. Nudge strategies significantly boosted the COVID-19 vaccine uptake rate (RR: 1.19, 95% CI [1.07, 1.33], p \u0026lt; 0.01). Subgroup analysis showed that there was a weak positive effect on vaccine uptake of social norms (RR: 2.04, 95% Cl [1.61, 2.57]), defaults (RR: 1.32, 95% CI [1.03, 1.69]), and salient reminders (RR: 1.19, 95% CI [1.04, 1.36]). Additionally, the effect of nudging interventions on COVID-19 vaccine uptake weakened over time(p \u0026lt; 0.0001). Most studies (9 of 10) involving vaccination intention outcomes showed positive or partially positive results.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion:\u003c/strong\u003e Nudging interventions can promote COVID-19 vaccination behavior and intentions, albeit with small magnitude, and need to be combined with other intervention strategies to promote vaccination.\u003c/p\u003e","manuscriptTitle":"Nudging vaccination against COVID-19: A systematic review and meta-analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-01-12 13:31:53","doi":"10.21203/rs.3.rs-2430314/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8dee205c-c263-4c0f-a550-a64551d64eb6","owner":[],"postedDate":"January 12th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-02-03T08:51:37+00:00","versionOfRecord":[],"versionCreatedAt":"2023-01-12 13:31:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2430314","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2430314","identity":"rs-2430314","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}