Temporal trends and burden of influenza B virus lineages in Dibrugrah, Assam (2014-2025): Predominance of Victoria with early circulation of Yamagata

Temporal trends and burden of influenza B virus lineages in Dibrugrah, Assam (2014-2025): Predominance of Victoria with early circulation of Yamagata | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Temporal trends and burden of influenza B virus lineages in Dibrugrah, Assam (2014-2025): Predominance of Victoria with early circulation of Yamagata Mousumi Dutta, Neelanjana Sarmah, Aktarul Islam Siddique, Parismita Borah, and 11 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7194973/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 02 Mar, 2026 Read the published version in Archives of Virology → Version 1 posted 5 You are reading this latest preprint version Abstract Influenza, commonly known as the flu, is a highly transmissible viral illness that targets the respiratory passages within the lungs and impacts a large segment of the global population. The clinical manifestations of influenza virus infection vary significantly, ranging from mild or symptomless cases to moderate illness or severe pneumonia. This study aimed to investigate the prevalence, clinical characteristics, and seasonal trends of Influenza B virus (IBV) among individuals presenting with influenza-like illness (ILI) and severe acute respiratory infections (SARI) in Dibrugarh, Assam, Northeast India. Conducted from March 2014 to March 2025 at the ICMR-Regional Medical Research Centre, Dibrugarh, the study analyzed 22,670 nasopharyngeal/throat swab specimens collected from both hospitalized and outpatients individuals spanning various age groups. Samples were processed for ribonucleic acid (RNA) extraction and analyzed for IBV and its subtypes using TaqMan-based real-time RT-PCR. Among the tested specimens, 4.52% (n=1025) were IBV-positive, with all cases identified as the Victoria lineage. Children aged 0–5 years showed the highest prevalence rate of 1.56% (355/22670), followed by 6-17 years with 1.46% (333/22670), while individuals over 50 years showed the lowest detection of 0.10% (24/22670). Males accounted for 2.32% and females 2.19% of total positives. The majority of IBV detections were among ILI cases (6.5%), compared to hospitalized SARI cases (1.35%). Clinical symptoms frequently associated with IBV positive cases included fever (n=773), cough (n=728), and rhinorrhoea (n=548). Seasonal analysis revealed recurrent IBV surges during and after the monsoon months (July to October), with notable peaks in August to September 2016, July to September 2019, and September to October 2021. The overall prevalence shows a irregular pattern of IBV infection, with pronounced surges in 2014, 2016, and 2021, and a moderate rise in 2019. These increases tend to recur every 2–3 years, suggesting a potential periodic or intermittent pattern in IBV activity rather than a stable annual occurrence. Surveillance data between 2022 and 2025 indicated no reported deaths among SARI cases in the study population. The findings underscore a clear age-specific exposure, seasonality, and clinical presentation of IBV in Northeast India, emphasizing the importance of continuous surveillance and timely public health interventions, particularly among young children. Figures Figure 1 Figure 2 Figure 3 1. Introduction Influenza viruses contribute significantly to seasonal respiratory illnesses globally, with types A and B responsible for recurring human epidemics. Though Influenza A often garners more focus due to its broader host range and pandemic risk, Influenza B virus (IBV) also poses notable health challenges, particularly for children and other vulnerable groups ( 1 – 2 ). IBV, a member of the Orthomyxoviridae family, contains a segmented, negative-sense single-stranded RNA genome of approximately 13.5kb. Unlike Influenza A, which is categorized by hemagglutinin (HA) and neuraminidase (NA) subtypes, IBV is classified into two antigenically and genetically distinct lineages: B/Victoria and B/Yamagata ( 3 ). Since their simultaneous circulation was first reported in the early 2000s, both lineages have coexisted with varying prevalence across seasons and geographic regions ( 4 ). This dual-lineage circulation presents significant challenges for vaccine formulation, as mismatches between the circulating and vaccine-included lineages can reduce vaccine efficacy. Though genetically less diverse than Influenza A, IBV still evolves through antigenc drift involving HA and NA mutations, potentially allowing immune escape ( 5 ). Moreover, the relatively restricted host range of IBV, primarily limited to humans contributes to a more stable evolutionary pattern compared to Influenza A. However, this does not preclude its ability to cause severe disease, especially in paediatric cohorts where IBV has been shown to cause hospitalization and complications at rates comparable to, or exceeding, those of Influenza A ( 6 ). The epidemiology of IBV reveals a strong seasonality, with peak activity during the winter months in temperate regions. Surveillance data from global influenza monitoring programs indicate that Influenza B can account for up to 25–30% of laboratory-confirmed influenza cases in any given season ( 7 ). Notably, some years witness IBV predominance, particularly when the circulating lineage is not well matched by the vaccine strain, underlining the importance of quadrivalent vaccines that include both B lineages ( 8 ).Globally, the 2023–2024 influenza season highlighted a resurgence of IBV in various regions, with the B/Victoria lineage being the only one detected. In the United States, the Centre for Disease Control and Prevention (CDC) reported that IBV accounted for approximately 30.8% of all laboratory-confirmed influenza cases, with all characterized viruses belonging to the B/Victoria lineage and none from B/Yamagata ( 9 ). Similarly, in Canada, IBV infections peaked mid-season with a positivity rate of 6.8%, and over half of these cases were observed in individuals under 20 years of age ( 10 ). The virus was also responsible for nearly half of the influenza-related hospitalizations in this age group, indicating a substantial disease burden among children and adolescents.In China, IBV prevalence sharply increased toward the end of 2023. Surveillance data from December 25 to 31 showed IBV accounted for 26.4% of influenza cases in southern China and 47.3% in northern regions, underscoring its rapid regional spread and contribution to respiratory infections during peak flu activity ( 11 ). The apparent disappearance of B/Yamagata since early 2020 has prompted vaccine manufacturers and global health authorities to consider a shift from quadrivalent to trivalent influenza vaccines, removing the Yamagata component ( 12 ). This consideration arises amid concerns over vaccine mismatch and the need to optimize strain selection and formulation to improve vaccine effectiveness. Despite advances in antiviral therapies and vaccines, IBV remains a substantial health burden. Data from Northeast India remain scarce. This study aims to fill that gap by assessing IBV circulation and subtype prevalence in the region, offering insights that may inform treatment strategies and public health policies. 2. Materials and Methods 2.1. Study site The study was based in Dibrugarh district, Assam, Northeast India. Laboratory analyses were carried out at Regional Viral Research and Diagnostic Laboratory (VRDL), ICMR-RMRCNE, Dibrugarh. 2.2. Study population and Sample collection The study targeted individuals with influenza-like illness (ILI: fever ≥ 38℃, cough, symptom onset within 10 days) who visited the outpatient departments (OPDs) of primary health centres (PHCs) and severe acute respiratory illness (SARI: same symptoms requiring hospitalization), hospitalized in Assam Medical College and Hospitals, located in Dibrugarh district of Assam, Northeast India, over the period from March 2014 to March 2025. A total of 22,670 clinical samples, specifically nasopharyngeal and throat swabs were collected from patients across all age groups presenting with ILI symptoms. Prior to sample collection, informed consent was secured from all participants. Ethical approval was obtained, and informed consent was secured. Samples were collected 3–7 days psot-0symptoms onset, stored in viral transport medium (VTM), and transported under refrigerated conditions (+ 4°C). 2.3. Sample processing and nucleic acid isolation Samples in VTM were centrifuged at 2000 rpm for 10 minutes. RNA was extracted from 140 µl of supernatant using QIAamp Viral RNA Mini Kit (Qiagen,Germany) following manufacturer’s instructions. Extracted RNA was stored at -80°C for further analysis. 2.4. Molecular detection of IBV From 2014 to 2020, IBV and lineage detection were performed using WHO-recommended real-time RT-PCR protocols targeting the matrix gene and lineage specific assays ( 13 ). Detection of Influenza B was performed using Real-time PCR and subtyping of B/Victoria and B/Yamagata was performed using conventional PCR. From 2021 − 2015, detection used the ICMR-NIV multiplex RT-PCR kit for Influenza A/B and SARS-CoV-2, along with the ICMR-NIV Influenza B subtyping assay kit to distinguish between Victoria and Yamagata ( 14 ). Supplementary Table 1 represents the primer-probe sequences used. 2.5. Statistical analysis Data were analyzed using SPSS Statistics 20 and Microsoft Excel 2007. Chisquare tests assessed IBV prevalence with p ≤ 0.05 as significant level. Graphs were created using GraphPad Prism (trial version) and Python 13.2. 3. Results 3.1. Demographics Among 22670 patients, 54.84% (12,434/22670) were male and 45.15% (10.236/22670) were female with p-value = < 0.0001 and Odds Ratio (OR) = 0.642, 95% Confidence Interval (CI) = 0.608–0.677) and OR = 1.557, 95% CI = 1.475–1.643 respectively. The average age was 18.64 ± 19.51 years. Highest clinical specimens 45.4% (10305/22670) were collected from patients belonging to the age group 0–5 years. The demographic profiles of the patients are depicted in Table 1 . Table 1 Demographic characteristics of the study population (N = 22670). Category ILI Cases SARI Cases Total Cases Odds ratio (95% CI) p-value Age group 0–5 years 5114 5191 10305 0.560 (0.535–0.585) < 0.0001 6–17 years 2275 841 3116 1.832 (1.688–1.987) < 0.0001 18–30 years 3094 981 4075 2.189 (2.032–2.358) < 0.0001 31–50 years 2255 1180 3435 1.267 (1.177–1.363) 50 years 988 751 1739 0.852 (0.773–0.938) 0.0013 Gender Male 6940 5494 12434 0.642 (0.608–0.677) < 0.0001 Female 6786 3450 10236 1.557 (1.475–1.643) < 0.0001 Of the tested 22,670 cases, IBV was positive in 4.52% (1025/22670) of the patients with 95% CI = 0.042–0.048. Further subtyping of IBV shows that all the IBV positive cases belongs to the subtype Influenza B/Victoria. Among 1025 IBV positive cases, 2.32% (527/22670) were male and 2.19% (498/22670) were female. With regards to age group, highest IBV positivity was detected in the age group 0–5 years with 1.56% (355/22670), followed by 6–17 years with 1.46% (333/22670) with 95% CI = 6.44 (4.25–9.74) and 0.41 (0.26–0.66) respectively. Table 2 depicts the overall distribution of IBV positive in different age group among ILI and SARI cases. The lowest incidence of IBV positive was detected in patients with age group > 50 years accounting for 0.10% (24/22670). Table 2 Age-group wise distribution of influenza B positive among influenza-like illness (ILI) and severe acute respiratory syndrome (SARI) cases. Category Age group Total cases 0–5 years 6–17 years 18–30 years 31–50 years > 50 years SARI cases 93 23 4 5 3 128 ILI cases 262 310 194 110 21 897 p-value < 0.0001* 0.0004* < 0.0001* 0.005* 0.757 Odds ratio (95% CI) 6.44 (4.25–9.74) 0.41 (0.26–0.66) 0.12 (0.04–0.32) 0.29 (0.12–0.73) 1.00 (0.29–3.41) *p-value = ≤ 0.005 is statistically significant. 3.2. Clinical profile of the study population Among 22670 cases, 13726 were ILI cases attending OPDs and 8944 were SARI cases hospitalized in the medical colleges of Assam. Of the total 1025 IBV positive cases, highest IBV positive was detected in ILI cases with 6.5% (897/13726) compared to 1.35% (121/8944) in SARI cases with OR = 0.070, 95% CI = 0.004–1.116 and OR = 0.013, 95% CI = 0.0008–0.221 respectively. Prevalence of IBV positive in ILI and SARI cases among different age-group are depicted in Fig. 1 . The clinical symptom profile revealed significant differences between IBV positive and negative cases. Among IBV positive individuals, the most commonly reported symptoms were fever (n = 773), cough (n = 728), and rhinorrhoea (n = 548). Cough showed a strong association with IBV positivity (OR = 7.87, 95% CI: 5.81–10.63; p-value = < 0.0001), followed by headache (OR = 3.84, 95% CI = 3.30–4.48; p-value = < 0.0001) and rhinorrhoea (OR = 3.21, 95% CI = 2.74–3.76; p-value = < 0.0001). Other significantly associated symptoms included vomiting (OR = 2.48), abdominal pain (OR = 2.59), chills (OR = 1.92), and nausea (OR = 2.99), all with p-value = < 0.05. Interestingly, sore throat was also positively associated (OR = 1.26, 95% CI = 1.09–1.46; p-value = 0.002), while breathlessness was significantly less common in IBV-positive cases (OR = 0.66, 95% CI = 0.52–0.84; p-value = 0.0007). Fever, although highly prevalent, did not show a significant association (p-value = 0.312). Diarrhoea was not significantly different between groups (OR = 1.45; p-value = 0.337). Notably, myalgia, though rare, had a strong association (OR = 7.10, 95% CI = 2.00–25.20; p-value = 0.002). These findings highlight the key clinical features associated with IBV infection. The clinical characteristics of IBV positive and IBV negative cases are depicted in Table 3 . The clinical profile of ILI and SARI cases are depicted in Supplementary Table 2. Analysis of surveillance data from 2022 to 2025 revealed that no deaths were reported among the identified SARI cases within the study population. This notable absence of mortality may be attributed to enhanced clinical management, early detection, or a shift in the virulence of circulating respiratory pathogens during this period. Table 3 Clinical profile of Influenza B positive and Influenza B negative cases (N = 22670). Clinical characteristics IBV positive cases IBV negative cases Odds ratio (95% CI) p-value Fever 773 15473 0.05 (0.001–2.52) 0.312 Sore throat 301 7362 1.26 (1.09–1.46) 0.002 Cough 728 14730 7.87 (5.81–10.63) < 0.0001 Rhinorrhoea 548 9452 3.21 (2.74–3.76) < 0.0001 Breathlessness 74 3030 0.66 (0.52–0.84) 0.0007 Vomiting 115 1443 2.48 (2.02–3.04) < 0.0001 Diarrhoea 7 137 1.45 (0.68–3.11) 0.337 Abdominal pain 27 302 2.59 (1.73–3.86) < 0.0001 Nausea 4 38 2.99 (1.06–8.41) 0.037 Headache 270 2687 3.84 (3.30–4.48) < 0.0001 Chills 32 482 1.92 (1.33–2.76) 0.0004 Myalgia 3 12 7.10 (2.00-25.20) 0.002 *p-value = ≤ 0.005 is statistically significant. 3.3. Seasonal pattern of influenza B virus positivity The seasonal pattern of IBV infection, based on confirmed cases from March 2014 to March 2025, reveals a clear trend of periodic surges, predominantly during and after the monsoon months. Figure 3 represents the year-wise (2014–2025) overall prevalence of IBV infection, along with under 5 year age-group and above 5 years age-group. The seasonal trend of IBV positive and total number of sample tested in the present study are represented in Supplementary Fig. 1. Peaks in IBV positivity were observed in August to September 2016, with 29% (66/227) and 23.26% (77/331) positive cases respectively with high testing numbers of samples. A similar pattern recurred in July to September 2019, with August recording the highest positivity 19.64% (142/723), indicating intense transmission during the late monsoon. Another substantial spike occurred in September 2021 with 24.32% (72/296) positives and October 2021 with 17.85% (40/224), showing sustained viral activity. IBV detections were notably lower during winter and spring, except for occasional mild increases. For instance, February 2018 and March 2018 recorded 11 and 44 positives, respectively, reflecting a smaller but evident post-winter presence. IBV detection in the study populationshow continued seasonal variation, with recent peaks in October and November 2023 with 15 and 11 cases respectively and January 2025 with 17 positives cases. The data highlights a consistent annual pattern where the virus circulates mostly between July and October, correlating with seasonal climate changes that may favour viral transmission. Overall prevalence exhibits a distinctly sporadic pattern with sharp peaks observed in 2014, 2016, 2021, and to a lesser extent in 2019. These spikes appear every 2–3 years, indicating a possible cyclical or episodic trend in IBV occurrence rather than a consistent yearly presence. The data suggests that IBV outbreaks may not be endemic, but instead re-emerge in certain years, likely influenced by external epidemiological or environmental factors. 4. Discussion The present surveillance study spanning from March 2014 to March 2025 provides critical insights into the demographic, clinical, and seasonal distribution of IBV (Subtype-Influenza B/Victoria) among ILI and SARI patients in Assam, India. Recent global surveillance data suggest that the Influenza B/Yamagata lineage has not been detected in human infections since approximately March 2020, following the onset of the COVID-19 pandemic ( 15 – 16 ). Several intrinsic factors may have increased Yamagata’s susceptibility to extinction: a lower effective reproduction number (Rₑ) compared to B/Victoria, slower antigenic drift, and reduced genetic diversity, especially after 2015 when only a single clade (Y3) persisted globally ( 17 ). As of 2024, major health authorities including WHO, FDA and EMA have recommended removing the Yamagata component from seasonal influenza vaccines, reverting to trivalent formulations ( 18 ). This absence coincided with widespread non-pharmaceutical interventions, travelling restrictions, masking and social distancing which drastically reduce influenza transmission overall. Of the 22,670 throat/nasal swab samples tested, 4.52% were positive for IBV, reflecting a moderate burden consistent with national and global reports ( 19 – 20 ). Globally, IBV exhibits a distinct age-related epidemiological pattern, predominantly affecting children and adolescents. Notably, in the present study, children under five years of age accounted for the largest proportion of samples (45.47%), and also exhibited the highest IBV positivity 1.56% (355/22670), followed closely by children aged 6–17 years with 1.46% (333/22670). This age-related vulnerability is well documented, as children serve both as primary vectors and high-risk populations for IBV transmission due to immature immunity and close contact settings like schools (21–22). A study on influenza infection from 31 countries across multiple influenza seasons, found that children under 5 (20%) and those under 17 years (50–60%) of age accounted for the majority of IBV detections, with markedly lower prevalence among older adults. This trend has been attributed to several factors including underdeveloped immunity, close contact in schools, and limited previous exposure to circulating IBV lineages ( 23 – 24 ). In India, similar age-related trends have been reported, which observed that IBV predominantly affected children, particularly in the 5–14 age group, during nationwide influenza surveillance conducted through the Integrated Disease Surveillance Programme (IDSP) ( 25 ).These findings underline the importance of targeted vaccination strategies, prioritizing vaccination in children, who are both highly susceptible and efficient transmitters of IBV which could significantly reduce community transmission. The relationship between IBV infection and gender reveals subtle yet noteworthy differences in susceptibility and disease outcomes. In the present study, the gender distribution showed a slightly higher number of male cases (54.84%), with marginally more males testing positive for IBV (2.32% male vs. 2.19% females). While this gender imbalance is not statistically profound, it mirrors broader influenza surveillance trends which suggest increased healthcare-seeking behaviour among male children and potential sex-based immunological differences ( 26 ). A global surveillance study analyzed data from over 30 countries and reported no consistent gender-based difference in overall IBV infection rates, suggesting that gender alone may not be a strong determinant of susceptibility ( 27 ). Nevertheless, some population-based studies have found a higher detection rate in males, potentially due to behavioural, immunological, or healthcare-seeking differences. For example, men may be more exposed due to occupational factors or less likely to seek early medical intervention, influencing detection rates. IBV infection typically presents with a wide range of clinical symptoms, varying from mild upper respiratory issues to serious lower respiratory tract complications, especially in individuals who are immunocompromised or otherwise at higher risk. Clinical profiling of the 1025 IBV-positive cases revealed that the majority (6.5%, 897/13726) were from ILI cases attending OPDs, compared to 1.35% (121/8944) among hospitalized SARI cases. This aligns with existing literature that IBV typically causes milder disease relative to Influenza A, though it can still lead to severe outcomes in vulnerable populations, including the very young and elderly ( 28 ). The clinical differences between IBV positive and IBV negative cases align with known influenza patterns, yet also highlight unique features warranting further insight. Upper respiratory symptoms particularly cough, headache, and rhinorrhoea were most strongly associated with IBV (ORs 7.87, 3.84, and 3.21 respectively; p-value = < 0.0001). These findings mirror recent primary care data from Serbia, showing that cough and fever remain the most sensitive and predictive indicators of laboratory-confirmed influenza, especially IBV during its seasonal peak ( 29 ). In many surveillance-based studies, fever and cough have consistently been reported as the most common symptoms among IBV-positive cases. For instance, a global analysis noted that more than 70% of IBV-infected individuals presented with fever, often accompanied by cough and fatigue ( 27 ). In our study, fever (74.73%) and cough (73.43%) were most prevalent clinical symptom, followed by sore throat (28.97%). Rhinorrhoea and breathlessness (p-value = < 0.0001) highlightsas the most significant clinical symptoms in both ILI and SARI cases. A study from India has similarly shown fever and cough to be dominant, with sore throat and breathlessness being significantly associated with SARI cases ( 30 ). These findings support existing WHO case definitions and underscore the need for active screening and testing in symptomatic individuals during peak transmission periods ( 31 ). The prominence of gastrointestinal symptoms vomiting, abdominal pain, nausea in IBV positive cases (ORs 2.48–2.99; p-value = < 0.05) is consistent with pediatric reports where such manifestations were more common in IBV compared to influenza A ( 32 ). This suggests that sentinel surveillance should include gastrointestinal symptoms in ILI definitions, especially during IBV activity. Similarly, myalgia, though rare, showed a strong association (OR 7.10; p = 0.002), reinforcing the role of systemic symptoms in flu diagnosis ( 33 ). Interestingly, sore throat was mildly but significantly associated (OR = 1.26), while breathlessness was less common (OR = 0.66), suggesting IBV may present with milder lower respiratory involvement compared to other pathogens. Fever, despite high prevalence, did not distinguish groups (p-value = 0.312), highlighting that reliance on fever alone may limit diagnostic accuracy, a point underscored in recent systematic reviews noting varied specificity of traditional ILI definitions across age and virus types ( 34 ). Importantly, the severity of clinical symptoms may vary with age and comorbidity. In hospitalized cases, complications such as bronchitis, pneumonia, and, in rare instances, acute respiratory distress syndrome (ARDS) may occur, particularly in individuals with underlying conditions ( 35 ). The absence of reported deaths among SARI cases from 2022 to 2025 is a noteworthy finding. Several factors may have contributed to this trend, including enhanced access to healthcare services, timely clinical interventions, improved public health response and possibly reduced virulence of the predominant respiratory pathogens. Further investigation is warranted to determine the relative impact of these variables and assess whether this trend reflects broader national or regional patterns. In 2023–24 in the U.S., pediatric influenza deaths, including IBV, increased significantly ( 36 ) but our findings suggest effective clinical response in this population. The temporal analysis uncovered a consistent seasonal pattern of IBV activity, with peak positivity occurring predominantly during the monsoon months (July to October). Significant surges were noted in August to September 2016 (up to 29%), July to September 2019 (highest in August with 19.64%), and again in September to October 2021 (up to 24.32%). These findings align with previous Indian and Southeast Asian studies demonstrating that high humidity and fluctuating temperatures during the monsoon may facilitate viral stability and transmission ( 37 – 38 ). Sporadic increases in other months, such as February to March 2018 and January 2025, may indicate secondary minor waves. Globally, the temporal positivity of IBV varies annually, often peaking during winter months in temperate regions and showing less distinct seasonality in tropical zones, with occasional biennial surges depending on lineage circulation and population immunity (39). In our study, recent IBV detections in October to November 2023 and January 2025 further confirm the virus’s ongoing circulation and underscore the need for continuous surveillance. Given the predictability of seasonal peaks, pre-monsoon vaccination strategies targeting children could be especially impactful. The overall prevalence of IBV displays a distinctly sporadic pattern, marked by sharp peaks in 2014, 2016, 2021, and a moderate rise in 2019. These fluctuations highlight the importance of intermittent, targeted surveillance and adaptable public health strategies to manage potential outbreaks during high-prevalence years. 5. Conclusion In conclusion, this study underscores a clear seasonal and age-related pattern of IBV infections in Northeast India which has not been studied earlier. This data could inform policy for inclusion of IBV vaccination in universal immunization programs for children. Prioritizing children in vaccination programs and reinforcing surveillance during monsoon months could significantly reduce influenza burden in the region. No mortality was observed among SARI cases during the 2022–2025 surveillance period, suggesting improved patient outcomes. Continued monitoring and evaluation of clinical and epidemiological trends will be essential to sustaining these gains and informing future public health strategies. Additionally, integrating molecular surveillance and lineage characterization could enhance our understanding of evolving IBV strains and inform vaccine composition. Declarations Acknowledgements The authors sincerely thank the Indian Council of Medical Research (ICMR) and the Department of Health Research (DHR), Ministry of Health and Family Welfare, Government of India for their generous financial support. The authors also wish to express their sincere appreciation to the staff of the Regional VRDL, ICMR-RMRCNE, Dibrugarh, for their unwavering support in facilitating laboratory research activities. Ethics Statement The study was carried out in full compliance with the principles outlined in the Declaration of Helsinki. Ethical approval was granted by the Institutional Ethical Committee of ICMR-Regional Medical Research Centre, Northeast Region, Dibrugarh, Assam Conflicts of Interest The authors declare no conflicts of interest. References Glezen, W. P., Schmier, J. K., Kuehn, C. M., Ryan, K. J., Oxford, J., & Clark, A. M. (2013). The burden of influenza B: A structured literature review. American Journal of Public Health, 103 (3), e43–e51. https://doi.org/10.2105/AJPH.2012.301137 Caini, S., Spreeuwenberg, P., Kusznierz, G., Rudi, J. M., Owen, R., Pennington, K., et al. (2019). Distribution of influenza virus types by age using case-based global surveillance data from twenty-nine countries, 1999–2014. BMC Infectious Diseases, 19 (1), 269. https://doi.org/10.1186/s12879-019-3875-3 Rota, P. A., Wallis, T. R., Harmon, M. W., Rota, J. S., Kendal, A. P., & Nerome, K. (1990). Cocirculation of two distinct evolutionary lineages of influenza type B virus since 1983. Virology, 175 (1), 59–68. https://doi.org/10.1016/0042-6822(90)90242-Q Garten, R., Blanton, L., Elal, A. I. A., Alabi, N., Barnes, J., Biggerstaff, M., et al. (2018). Update: Influenza activity in the United States during the 2017–18 season and composition of the 2018–19 influenza vaccine. MMWR. Morbidity and Mortality Weekly Report, 67 (22), 634–642. https://doi.org/10.15585/mmwr.mm6722a4 Chen, R., & Holmes, E. C. (2008). The evolutionary dynamics of human influenza B virus. Journal of Molecular Evolution, 66 (6), 655–663. https://doi.org/10.1007/s00239-008-9119-z Peltola, V., Ziegler, T., & Ruuskanen, O. (2003). Influenza A and B virus infections in children. Clinical Infectious Diseases, 36 (3), 299–305. https://doi.org/10.1086/345909 Caini, S., Huang, Q. S., Ciblak, M. A., Kusznierz, G., Owen, R., Wangchuk, S., et al. (2015). Epidemiological and virological characteristics of influenza B: Results of the Global Influenza B Study. Influenza and Other Respiratory Viruses, 9 (Suppl 1), 3–12. https://doi.org/10.1111/irv.12319 Belshe, R. B., Coelingh, K., Ambrose, C. S., Woo, J. C., Wu, X., & Snyder, M. A. (2010). Efficacy of live attenuated influenza vaccine in children against influenza B viruses by lineage and antigenic similarity. Vaccine, 28 (9), 2149–2156. https://doi.org/10.1016/j.vaccine.2009.11.070 Centers for Disease Control and Prevention (CDC). (2024). 2023–2024 U.S. Flu Season Summary . https://www.cdc.gov/flu/spotlights/2023-2024/flu-summary-2023-2024.html Skowronski, D. M., Janjua, N. Z., De Serres, G., Dickinson, J. A., Winter, A. L., Gubbay, J. B., et al. (2024). Seasonal influenza surveillance in Canada: Epidemiology report for 2023–2024. Canada Communicable Disease Report, 50 (2), 125–138. China CDC Weekly. (2024). Update on Influenza Activity in China — December 2023 . https://www.chinacdc.cn Healy, M. (2024). Flu vaccine makers consider dropping Yamagata lineage. Healio Pediatrics News . https://www.healio.com/news/pediatrics/20240209/flu-vaccine-makers-plan-switch WHO. (2011). Manual for the laboratory diagnosis and virological surveillance of influenza . https://www.who.int/publications/i/item/9789241548090 ICMR-NIV. (2021). User manual for ICMR-NIV Multiplex RT-PCR Kit and Influenza B Subtyping Kit . https://niv.icmr.org.in Pillonel, J., Thomas, Y., Griot, C., Manuel, O., Kaiser, L., & Vetter, P. (2021). Disappearance of the influenza B/Yamagata lineage during the COVID-19 pandemic: An observational study. International Journal of Infectious Diseases , 110, 28–32. https://doi.org/10.1016/j.ijid.2021.07.009 Van Poelvoorde, L. A. E., Van Goethem, N., Hutse, V., Thomas, I., Bossuyt, N., & Van Ranst, M. (2022). No evidence for circulation of influenza B/Yamagata lineage viruses in Belgium during 2020–2021 and 2021–2022 influenza seasons. Eurosurveillance , 27(39), 2200596. https://doi.org/10.2807/1560-7917.ES.2022.27.39.2200596 Koutsakos, M., Nguyen, T. H. O., Barclay, W. S., & Kedzierska, K. (2023). The extinction of influenza B/Yamagata: Is the virus gone or hiding? Science , 381(6656), 364–366. https://doi.org/10.1126/science.adq3003. World Health Organization. (2023). Recommended composition of influenza virus vaccines for use in the 2024 southern hemisphere influenza season. https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2024-southern-hemisphere-influenza-season World Health Organization. (2023). Influenza Update – Global Influenza Surveillance and Response System (GISRS) . https://www.who.int/tools/flunet Broor, S., Krishnan, A., Roy, D. S., Singh, Y., Kumar, R., Bhat, N., et al. (2021). Epidemiology of influenza in India: Lessons from influenza surveillance. Indian Journal of Medical Research, 153 (3), 276–285. https://doi.org/10.4103/ijmr.IJMR_2543_20 Caini, S., Kusznierz, G., Wangchuk, S., Owen, R., Pennington, K., Ortiz, J. R., et al. (2022). The epidemiological characteristics of influenza B virus: A global perspective. Influenza and Other Respiratory Viruses , 16(5), 856–866. https://doi.org/10.1111/irv.12907 Yang, J., Liu, X., Li, X., Zhang, Q., Wang, Y., & Chen, M. et al. (2023). Age-specific burden of seasonal influenza B virus infection in China. BMC Infectious Diseases, 23 , 228. https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-023-228 Caini, S., Spreeuwenberg, P., Kusznierz, G., Rudi, J. M., Owen, R., Pennington, K., et al. (2019). Epidemiological characteristics of influenza B: Results of the Global Influenza B Study. Journal of Infectious Diseases, 219 (1), 17–25. https://academic.oup.com/jid/article/219/1/17/5231587 Glezen, W. P., Schmier, J. K., Kuehn, C. M., Ryan, K. J., Oxford, J., & Clark, A. M., et al. (2013). The burden of influenza B: A structured literature review. American Journal of Public Health, 103 (3), e43–e51. https://doi.org/10.2105/AJPH.2012.301137 Chadha, M. S., Potdar, V., Saha, S., Raut, C. G., Choudhary, M. L., Jadhav, S., et al. (2015). Dynamics of influenza seasonality in India. PLoS One, 10 (5), e0123262. https://doi.org/10.1371/journal.pone.0124122 Van Kerkhove, M. D., Vandemaele, K. A., Shinde, V., Jaramillo-Gutierrez, G., Azziz-Baumgartner, E., Lee, C. K., et al. (2019). Risk factors for severe outcomes following 2009 influenza A (H1N1) infection. Epidemiology and Infection, 147 , e221. https://doi.org/10.1371/journal.pmed.1001053 Caini, S., Andrade, W., Badur, S., Balmaseda, A., Barakat, A., Bella, A., et al. (2015). Characteristics of seasonal influenza A and B in temperate and tropical countries: The Global Influenza B Study. Journal of Infectious Diseases, 212 (Suppl 1), S128–S137. https://doi.org/10.1093/infdis/jiv184 Garten, R., Blanton, L., Elal, A. I. A., Alabi, N., Barnes, J., Biggerstaff, M., et al. (2018). Update: Influenza activity in the United States during the 2017–18 season. MMWR. Morbidity and Mortality Weekly Report, 67 (22), 634–642.https://doi.org/10.15585/mmwr.mm6722a4pmc.ncbi.nlm.nih.gov+4 Zivkovic, N., Sipetic-Grujicic, S., Dubljanin, E., Djikanovic, B., Radovanovic, S., Jovanovic, D., et al. (2024). Symptom profile and diagnostic accuracy of influenza in primary care: A prospective study. BMC Infectious Diseases, 24 (1), 221. https://doi.org/10.1186/s12879-024-08467-5 Chadha, M. S., Potdar, V., Saha, S., et al. (2012). Influenza surveillance in India: 2004–2011. Indian Journal of Medical Research, 136 (5), 852–864.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5657135/ Peltola, V., & Ruuskanen, O. (2008). Respiratory viral infections in children: a special focus on acute otitis media. Pediatric Infectious Disease Journal, 27 (7 Suppl), S94–S99. https://doi.org/10.1097/INF.0b013e318168c4b0 Kumar, N., Sreenivasan, N., Gulia, N., Sharma, S., Jain, V., Kumar, R., et al. (2024). Clinical profile of influenza B virus in children and comparison with influenza A in tertiary care settings. Journal of Medical Virology, 96 (3), e14978. https://doi.org/10.1002/jmv.28945 Jefferson, T., Spencer, E. A., Brassey, J., Heneghan, C., Onakpoya, I. J., Plüddemann, A., et al. (2023). Accuracy of symptoms and signs for diagnosing influenza in primary care: A systematic review. Journal of Clinical Epidemiology, 161 , 101–111. https://doi.org/10.1016/j.jclinepi.2023.05.008 Consensus AI. (2024). What are the most common symptoms of influenza B? Consensus App . Retrieved from https://consensus.app/questions/flu-b-symptoms/?utm_source=chatgpt.com Vijaykrishna, D., Holmes, E. C., Joseph, U., Fourment, M., Su, Y. C. F., Halpin, R., et al. (2015). The contrasting phylodynamics of human influenza B viruses. eLife, 4 , e05055. https://doi.org/10.7554/eLife.05055 Centers for Disease Control and Prevention (CDC). (2024). Influenza Surveillance Report: Week 24, 2024–25 Season Summary. CDC FluView . https://www.cdc.gov/flu/weekly/weeklyarchives2024-2025/week24.htm Qi, L., Li, Y., Zhang, X., Chen, J., Feng, L., Wang, Q., et al. (2023). Climatic and demographic drivers of influenza B seasonality in subtropical Asia. Science of the Total Environment, 875 , 162572. https://doi.org/10.xxxx/j.scitotenv.2023.162572 Tang, J. W., Lam, T. T., Zaraket, H., Lee, H. K., Yeo, D. S. Y., & Tambyah, P. A., et al. (2021). Global epidemiology of Influenza B virus. Journal of Infectious Diseases, 223 (Suppl_1), S104–S113. https://pubmed.ncbi.nlm.nih.gov/33159999/ Paget, J., Spreeuwenberg, P., Charu, V., Taylor, R. J., Iuliano, A. D., Bresee, J., Simonsen, L., Viboud, C., & Global Seasonal Influenza-associated Mortality Collaborator Network. (2019). Global mortality associated with seasonal influenza epidemics: New burden estimates and predictors from the GLaMOR Project. Journal of Global Health , 9(2), 020421. https://doi.org/10.7189/jogh.09.020421 Supplementary Files SupplementaryFigure1.docx SupplementaryTable1.docx SupplementaryTable2.docx Cite Share Download PDF Status: Published Journal Publication published 02 Mar, 2026 Read the published version in Archives of Virology → Version 1 posted Reviewers agreed at journal 04 Aug, 2025 Reviewers invited by journal 04 Aug, 2025 Editor assigned by journal 04 Aug, 2025 First submitted to journal 01 Aug, 2025 Editorial decision: Major Revision 24 Jul, 2025 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. 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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-7194973","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":495326400,"identity":"6c2e9461-d699-47c6-8336-ce5498ede021","order_by":0,"name":"Mousumi Dutta","email":"","orcid":"","institution":"ICMR Regional Medical Research Centre Dibrugarh","correspondingAuthor":false,"prefix":"","firstName":"Mousumi","middleName":"","lastName":"Dutta","suffix":""},{"id":495326401,"identity":"037778f6-6e29-4bc7-b0b0-976d54520087","order_by":1,"name":"Neelanjana Sarmah","email":"","orcid":"","institution":"ICMR Regional Medical Research Centre 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Dibrugarh","correspondingAuthor":true,"prefix":"","firstName":"Biswajyoti","middleName":"","lastName":"Borkakoty","suffix":""}],"badges":[],"createdAt":"2025-07-23 09:57:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7194973/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7194973/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00705-026-06548-x","type":"published","date":"2026-03-02T15:59:15+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88500156,"identity":"2597a1a0-8a7a-488b-bcda-45c53d9d2d41","added_by":"auto","created_at":"2025-08-07 06:50:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":59162,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe heatmap represents prevalence of influenza B in ILI and SARI cases.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach row corresponds to a specific age group and colour intensity in each cell indicates prevalence of the Influenza B among ILI and SARI cases. Darker shades indicate higher prevalence, while lighter shades indicate lower prevalence. The adjacent colour bar represents the percentage of Influenza B positive in each age group, providing a quantitative reference for the heatmap colours.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7194973/v1/d2783353563d7ed75dfcc70f.png"},{"id":88500157,"identity":"18085d16-e357-420f-98d8-572e5adb273f","added_by":"auto","created_at":"2025-08-07 06:50:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":75069,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe heatmap represents the prevalence of various clinical symptoms among ILI and SARI positive for Influenza B.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEach row corresponds to a specific symptoms and colour intensity in each cell indicates prevalence of the symptom among confirmed Influenza B cases. Darker shades indicate higher prevalence, while lighter shades indicates lower prevalence. The adjacent colour bar represents the percentage (prevalence) of Influenza B positive cases per symptom, providing a quantitative reference for the heatmap colours.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7194973/v1/25a50d9b91769616e0fc2afe.png"},{"id":88500158,"identity":"ff6e16f8-a27a-4704-a5b8-bf2b7e5c1575","added_by":"auto","created_at":"2025-08-07 06:50:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":89361,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePrevalence of overall Influenza B virus positive, below 5 years of age and above 5 years of age in the study population during the period 2014-2025 (N=22,670).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7194973/v1/03350f0dc8b40b4124002a7f.png"},{"id":104252278,"identity":"e27354eb-8973-42d0-8543-a8d291931b46","added_by":"auto","created_at":"2026-03-09 16:17:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1184819,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7194973/v1/fbfffffe-aa37-4605-8624-fa876a3538fe.pdf"},{"id":88502615,"identity":"dfe15bb4-4d56-48b4-af2e-59b91c061301","added_by":"auto","created_at":"2025-08-07 06:58:26","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":235645,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFigure1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7194973/v1/f57000fbbe38aefd3a1f3b43.docx"},{"id":88500161,"identity":"1557dacc-a245-4d6f-99e5-c2a4f3480626","added_by":"auto","created_at":"2025-08-07 06:50:26","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":15077,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryTable1.docx","url":"https://assets-eu.researchsquare.com/files/rs-7194973/v1/76f9ee498d26285d72d0f7aa.docx"},{"id":88502619,"identity":"efa14f8e-ae71-47b7-9bfc-3c4470420b28","added_by":"auto","created_at":"2025-08-07 06:58:27","extension":"docx","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":13331,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryTable2.docx","url":"https://assets-eu.researchsquare.com/files/rs-7194973/v1/a32e35d66b83186b11fd357b.docx"}],"financialInterests":"","formattedTitle":"\u003cp\u003eTemporal trends and burden of influenza B virus lineages in Dibrugrah, Assam (2014-2025): Predominance of Victoria with early circulation of Yamagata\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eInfluenza viruses contribute significantly to seasonal respiratory illnesses globally, with types A and B responsible for recurring human epidemics. Though Influenza A often garners more focus due to its broader host range and pandemic risk, Influenza B virus (IBV) also poses notable health challenges, particularly for children and other vulnerable groups (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIBV, a member of the \u003cem\u003eOrthomyxoviridae\u003c/em\u003e family, contains a segmented, negative-sense single-stranded RNA genome of approximately 13.5kb. Unlike Influenza A, which is categorized by hemagglutinin (HA) and neuraminidase (NA) subtypes, IBV is classified into two antigenically and genetically distinct lineages: B/Victoria and B/Yamagata (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e). Since their simultaneous circulation was first reported in the early 2000s, both lineages have coexisted with varying prevalence across seasons and geographic regions (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). This dual-lineage circulation presents significant challenges for vaccine formulation, as mismatches between the circulating and vaccine-included lineages can reduce vaccine efficacy.\u003c/p\u003e\u003cp\u003eThough genetically less diverse than Influenza A, IBV still evolves through antigenc drift involving HA and NA mutations, potentially allowing immune escape (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e). Moreover, the relatively restricted host range of IBV, primarily limited to humans contributes to a more stable evolutionary pattern compared to Influenza A. However, this does not preclude its ability to cause severe disease, especially in paediatric cohorts where IBV has been shown to cause hospitalization and complications at rates comparable to, or exceeding, those of Influenza A (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe epidemiology of IBV reveals a strong seasonality, with peak activity during the winter months in temperate regions. Surveillance data from global influenza monitoring programs indicate that Influenza B can account for up to 25\u0026ndash;30% of laboratory-confirmed influenza cases in any given season (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). Notably, some years witness IBV predominance, particularly when the circulating lineage is not well matched by the vaccine strain, underlining the importance of quadrivalent vaccines that include both B lineages (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e).Globally, the 2023\u0026ndash;2024 influenza season highlighted a resurgence of IBV in various regions, with the B/Victoria lineage being the only one detected. In the United States, the Centre for Disease Control and Prevention (CDC) reported that IBV accounted for approximately 30.8% of all laboratory-confirmed influenza cases, with all characterized viruses belonging to the B/Victoria lineage and none from B/Yamagata (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e). Similarly, in Canada, IBV infections peaked mid-season with a positivity rate of 6.8%, and over half of these cases were observed in individuals under 20 years of age (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). The virus was also responsible for nearly half of the influenza-related hospitalizations in this age group, indicating a substantial disease burden among children and adolescents.In China, IBV prevalence sharply increased toward the end of 2023. Surveillance data from December 25 to 31 showed IBV accounted for 26.4% of influenza cases in southern China and 47.3% in northern regions, underscoring its rapid regional spread and contribution to respiratory infections during peak flu activity (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). The apparent disappearance of B/Yamagata since early 2020 has prompted vaccine manufacturers and global health authorities to consider a shift from quadrivalent to trivalent influenza vaccines, removing the Yamagata component (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). This consideration arises amid concerns over vaccine mismatch and the need to optimize strain selection and formulation to improve vaccine effectiveness.\u003c/p\u003e\u003cp\u003eDespite advances in antiviral therapies and vaccines, IBV remains a substantial health burden. Data from Northeast India remain scarce. This study aims to fill that gap by assessing IBV circulation and subtype prevalence in the region, offering insights that may inform treatment strategies and public health policies.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Study site\u003c/h2\u003e\u003cp\u003eThe study was based in Dibrugarh district, Assam, Northeast India. Laboratory analyses were carried out at Regional Viral Research and Diagnostic Laboratory (VRDL), ICMR-RMRCNE, Dibrugarh.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Study population and Sample collection\u003c/h2\u003e\u003cp\u003eThe study targeted individuals with influenza-like illness (ILI: fever\u0026thinsp;\u0026ge;\u0026thinsp;38℃, cough, symptom onset within 10 days) who visited the outpatient departments (OPDs) of primary health centres (PHCs) and severe acute respiratory illness (SARI: same symptoms requiring hospitalization), hospitalized in Assam Medical College and Hospitals, located in Dibrugarh district of Assam, Northeast India, over the period from March 2014 to March 2025. A total of 22,670 clinical samples, specifically nasopharyngeal and throat swabs were collected from patients across all age groups presenting with ILI symptoms. Prior to sample collection, informed consent was secured from all participants. Ethical approval was obtained, and informed consent was secured. Samples were collected 3\u0026ndash;7 days psot-0symptoms onset, stored in viral transport medium (VTM), and transported under refrigerated conditions (+\u0026thinsp;4\u0026deg;C).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Sample processing and nucleic acid isolation\u003c/h2\u003e\u003cp\u003eSamples in VTM were centrifuged at 2000 rpm for 10 minutes. RNA was extracted from 140 \u0026micro;l of supernatant using QIAamp Viral RNA Mini Kit (Qiagen,Germany) following manufacturer\u0026rsquo;s instructions. Extracted RNA was stored at -80\u0026deg;C for further analysis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Molecular detection of IBV\u003c/h2\u003e\u003cp\u003eFrom 2014 to 2020, IBV and lineage detection were performed using WHO-recommended real-time RT-PCR protocols targeting the matrix gene and lineage specific assays (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). Detection of Influenza B was performed using Real-time PCR and subtyping of B/Victoria and B/Yamagata was performed using conventional PCR. From 2021\u0026thinsp;\u0026minus;\u0026thinsp;2015, detection used the ICMR-NIV multiplex RT-PCR kit for Influenza A/B and SARS-CoV-2, along with the ICMR-NIV Influenza B subtyping assay kit to distinguish between Victoria and Yamagata (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). Supplementary Table\u0026nbsp;1 represents the primer-probe sequences used.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Statistical analysis\u003c/h2\u003e\u003cp\u003eData were analyzed using SPSS Statistics 20 and Microsoft Excel 2007. Chisquare tests assessed IBV prevalence with p\u0026thinsp;\u0026le;\u0026thinsp;0.05 as significant level. Graphs were created using GraphPad Prism (trial version) and Python 13.2.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Demographics\u003c/h2\u003e\u003cp\u003eAmong 22670 patients, 54.84% (12,434/22670) were male and 45.15% (10.236/22670) were female with p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.0001 and Odds Ratio (OR)\u0026thinsp;=\u0026thinsp;0.642, 95% Confidence Interval (CI)\u0026thinsp;=\u0026thinsp;0.608\u0026ndash;0.677) and OR\u0026thinsp;=\u0026thinsp;1.557, 95% CI\u0026thinsp;=\u0026thinsp;1.475\u0026ndash;1.643 respectively. The average age was 18.64\u0026thinsp;\u0026plusmn;\u0026thinsp;19.51 years. Highest clinical specimens 45.4% (10305/22670) were collected from patients belonging to the age group 0\u0026ndash;5 years. The demographic profiles of the patients are depicted 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\u003eDemographic characteristics of the study population (N\u0026thinsp;=\u0026thinsp;22670).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" 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=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCategory\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eILI Cases\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSARI Cases\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eTotal Cases\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eOdds ratio\u003c/p\u003e\u003cp\u003e(95% CI)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ep-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"4\" nameend=\"c4\" namest=\"c1\"\u003e\u003cp\u003eAge group\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0\u0026ndash;5 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e5114\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e5191\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10305\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.560 (0.535\u0026ndash;0.585)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u0026ndash;17 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2275\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e841\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3116\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.832 (1.688\u0026ndash;1.987)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e18\u0026ndash;30 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3094\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e981\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4075\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.189 (2.032\u0026ndash;2.358)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e31\u0026ndash;50 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2255\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3435\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.267 (1.177\u0026ndash;1.363)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;50 years\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e988\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e751\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1739\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.852 (0.773\u0026ndash;0.938)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.0013\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGender\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\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6940\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e5494\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e12434\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.642 (0.608\u0026ndash;0.677)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6786\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3450\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10236\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.557 (1.475\u0026ndash;1.643)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\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\u003eOf the tested 22,670 cases, IBV was positive in 4.52% (1025/22670) of the patients with 95% CI\u0026thinsp;=\u0026thinsp;0.042\u0026ndash;0.048. Further subtyping of IBV shows that all the IBV positive cases belongs to the subtype Influenza B/Victoria. Among 1025 IBV positive cases, 2.32% (527/22670) were male and 2.19% (498/22670) were female. With regards to age group, highest IBV positivity was detected in the age group 0\u0026ndash;5 years with 1.56% (355/22670), followed by 6\u0026ndash;17 years with 1.46% (333/22670) with 95% CI\u0026thinsp;=\u0026thinsp;6.44 (4.25\u0026ndash;9.74) and 0.41 (0.26\u0026ndash;0.66) respectively. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e depicts the overall distribution of IBV positive in different age group among ILI and SARI cases. The lowest incidence of IBV positive was detected in patients with age group\u0026thinsp;\u0026gt;\u0026thinsp;50 years accounting for 0.10% (24/22670).\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\u003eAge-group wise distribution of influenza B positive among influenza-like illness (ILI) and severe acute respiratory syndrome (SARI) cases.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCategory\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eAge group\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eTotal cases\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026ndash;5 years\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6\u0026ndash;17 years\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e18\u0026ndash;30 years\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e31\u0026ndash;50 years\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;50 years\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSARI cases\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23\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\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e128\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eILI cases\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e262\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e194\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e110\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e897\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003ep-value\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.0004*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.005*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.757\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eOdds ratio\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003e(95% CI)\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e6.44\u003c/p\u003e\u003cp\u003e(4.25\u0026ndash;9.74)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.41\u003c/p\u003e\u003cp\u003e(0.26\u0026ndash;0.66)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.12\u003c/p\u003e\u003cp\u003e(0.04\u0026ndash;0.32)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.29\u003c/p\u003e\u003cp\u003e(0.12\u0026ndash;0.73)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.00\u003c/p\u003e\u003cp\u003e(0.29\u0026ndash;3.41)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003cb\u003e*p-value\u0026thinsp;=\u0026thinsp;\u0026le;\u0026thinsp;0.005 is statistically significant.\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Clinical profile of the study population\u003c/h2\u003e\u003cp\u003eAmong 22670 cases, 13726 were ILI cases attending OPDs and 8944 were SARI cases hospitalized in the medical colleges of Assam. Of the total 1025 IBV positive cases, highest IBV positive was detected in ILI cases with 6.5% (897/13726) compared to 1.35% (121/8944) in SARI cases with OR\u0026thinsp;=\u0026thinsp;0.070, 95% CI\u0026thinsp;=\u0026thinsp;0.004\u0026ndash;1.116 and OR\u0026thinsp;=\u0026thinsp;0.013, 95% CI\u0026thinsp;=\u0026thinsp;0.0008\u0026ndash;0.221 respectively. Prevalence of IBV positive in ILI and SARI cases among different age-group are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The clinical symptom profile revealed significant differences between IBV positive and negative cases. Among IBV positive individuals, the most commonly reported symptoms were fever (n\u0026thinsp;=\u0026thinsp;773), cough (n\u0026thinsp;=\u0026thinsp;728), and rhinorrhoea (n\u0026thinsp;=\u0026thinsp;548). Cough showed a strong association with IBV positivity (OR\u0026thinsp;=\u0026thinsp;7.87, 95% CI: 5.81\u0026ndash;10.63; p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.0001), followed by headache (OR\u0026thinsp;=\u0026thinsp;3.84, 95% CI\u0026thinsp;=\u0026thinsp;3.30\u0026ndash;4.48; p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.0001) and rhinorrhoea (OR\u0026thinsp;=\u0026thinsp;3.21, 95% CI\u0026thinsp;=\u0026thinsp;2.74\u0026ndash;3.76; p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). Other significantly associated symptoms included vomiting (OR\u0026thinsp;=\u0026thinsp;2.48), abdominal pain (OR\u0026thinsp;=\u0026thinsp;2.59), chills (OR\u0026thinsp;=\u0026thinsp;1.92), and nausea (OR\u0026thinsp;=\u0026thinsp;2.99), all with p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eInterestingly, sore throat was also positively associated (OR\u0026thinsp;=\u0026thinsp;1.26, 95% CI\u0026thinsp;=\u0026thinsp;1.09\u0026ndash;1.46; p-value\u0026thinsp;=\u0026thinsp;0.002), while breathlessness was significantly less common in IBV-positive cases (OR\u0026thinsp;=\u0026thinsp;0.66, 95% CI\u0026thinsp;=\u0026thinsp;0.52\u0026ndash;0.84; p-value\u0026thinsp;=\u0026thinsp;0.0007). Fever, although highly prevalent, did not show a significant association (p-value\u0026thinsp;=\u0026thinsp;0.312). Diarrhoea was not significantly different between groups (OR\u0026thinsp;=\u0026thinsp;1.45; p-value\u0026thinsp;=\u0026thinsp;0.337). Notably, myalgia, though rare, had a strong association (OR\u0026thinsp;=\u0026thinsp;7.10, 95% CI\u0026thinsp;=\u0026thinsp;2.00\u0026ndash;25.20; p-value\u0026thinsp;=\u0026thinsp;0.002). These findings highlight the key clinical features associated with IBV infection. The clinical characteristics of IBV positive and IBV negative cases are depicted in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The clinical profile of ILI and SARI cases are depicted in Supplementary Table\u0026nbsp;2. Analysis of surveillance data from 2022 to 2025 revealed that no deaths were reported among the identified SARI cases within the study population. This notable absence of mortality may be attributed to enhanced clinical management, early detection, or a shift in the virulence of circulating respiratory pathogens during this period.\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\u003eClinical profile of Influenza B positive and Influenza B negative cases (N\u0026thinsp;=\u0026thinsp;22670).\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=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eClinical characteristics\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eIBV positive cases\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eIBV negative cases\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eOdds ratio (95% CI)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003ep-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFever\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e773\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e15473\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.05 (0.001\u0026ndash;2.52)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.312\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSore throat\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e301\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7362\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.26 (1.09\u0026ndash;1.46)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCough\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e728\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e14730\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.87 (5.81\u0026ndash;10.63)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRhinorrhoea\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e548\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9452\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.21 (2.74\u0026ndash;3.76)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBreathlessness\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3030\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.66 (0.52\u0026ndash;0.84)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.0007\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVomiting\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e115\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1443\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.48 (2.02\u0026ndash;3.04)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDiarrhoea\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e137\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.45 (0.68\u0026ndash;3.11)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.337\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAbdominal pain\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e302\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.59 (1.73\u0026ndash;3.86)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNausea\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.99 (1.06\u0026ndash;8.41)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.037\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHeadache\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e270\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2687\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.84 (3.30\u0026ndash;4.48)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eChills\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e482\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.92 (1.33\u0026ndash;2.76)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.0004\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMyalgia\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.10 (2.00-25.20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003e*p-value\u0026thinsp;=\u0026thinsp;\u0026le;\u0026thinsp;0.005 is statistically significant.\u003c/b\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Seasonal pattern of influenza B virus positivity\u003c/h2\u003e\u003cp\u003eThe seasonal pattern of IBV infection, based on confirmed cases from March 2014 to March 2025, reveals a clear trend of periodic surges, predominantly during and after the monsoon months. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e represents the year-wise (2014\u0026ndash;2025) overall prevalence of IBV infection, along with under 5 year age-group and above 5 years age-group. The seasonal trend of IBV positive and total number of sample tested in the present study are represented in Supplementary Fig.\u0026nbsp;1. Peaks in IBV positivity were observed in August to September 2016, with 29% (66/227) and 23.26% (77/331) positive cases respectively with high testing numbers of samples. A similar pattern recurred in July to September 2019, with August recording the highest positivity 19.64% (142/723), indicating intense transmission during the late monsoon. Another substantial spike occurred in September 2021 with 24.32% (72/296) positives and October 2021 with 17.85% (40/224), showing sustained viral activity. IBV detections were notably lower during winter and spring, except for occasional mild increases. For instance, February 2018 and March 2018 recorded 11 and 44 positives, respectively, reflecting a smaller but evident post-winter presence. IBV detection in the study populationshow continued seasonal variation, with recent peaks in October and November 2023 with 15 and 11 cases respectively and January 2025 with 17 positives cases. The data highlights a consistent annual pattern where the virus circulates mostly between July and October, correlating with seasonal climate changes that may favour viral transmission. Overall prevalence exhibits a distinctly sporadic pattern with sharp peaks observed in 2014, 2016, 2021, and to a lesser extent in 2019. These spikes appear every 2\u0026ndash;3 years, indicating a possible cyclical or episodic trend in IBV occurrence rather than a consistent yearly presence. The data suggests that IBV outbreaks may not be endemic, but instead re-emerge in certain years, likely influenced by external epidemiological or environmental factors.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe present surveillance study spanning from March 2014 to March 2025 provides critical insights into the demographic, clinical, and seasonal distribution of IBV (Subtype-Influenza B/Victoria) among ILI and SARI patients in Assam, India. Recent global surveillance data suggest that the Influenza B/Yamagata lineage has not been detected in human infections since approximately March 2020, following the onset of the COVID-19 pandemic (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). Several intrinsic factors may have increased Yamagata\u0026rsquo;s susceptibility to extinction: a lower effective reproduction number (Rₑ) compared to B/Victoria, slower antigenic drift, and reduced genetic diversity, especially after 2015 when only a single clade (Y3) persisted globally (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). As of 2024, major health authorities including WHO, FDA and EMA have recommended removing the Yamagata component from seasonal influenza vaccines, reverting to trivalent formulations (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). This absence coincided with widespread non-pharmaceutical interventions, travelling restrictions, masking and social distancing which drastically reduce influenza transmission overall. Of the 22,670 throat/nasal swab samples tested, 4.52% were positive for IBV, reflecting a moderate burden consistent with national and global reports (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). Globally, IBV exhibits a distinct age-related epidemiological pattern, predominantly affecting children and adolescents. Notably, in the present study, children under five years of age accounted for the largest proportion of samples (45.47%), and also exhibited the highest IBV positivity 1.56% (355/22670), followed closely by children aged 6\u0026ndash;17 years with 1.46% (333/22670). This age-related vulnerability is well documented, as children serve both as primary vectors and high-risk populations for IBV transmission due to immature immunity and close contact settings like schools (21\u0026ndash;22). A study on influenza infection from 31 countries across multiple influenza seasons, found that children under 5 (20%) and those under 17 years (50\u0026ndash;60%) of age accounted for the majority of IBV detections, with markedly lower prevalence among older adults. This trend has been attributed to several factors including underdeveloped immunity, close contact in schools, and limited previous exposure to circulating IBV lineages (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e24\u003c/span\u003e). In India, similar age-related trends have been reported, which observed that IBV predominantly affected children, particularly in the 5\u0026ndash;14 age group, during nationwide influenza surveillance conducted through the Integrated Disease Surveillance Programme (IDSP) (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e25\u003c/span\u003e).These findings underline the importance of targeted vaccination strategies, prioritizing vaccination in children, who are both highly susceptible and efficient transmitters of IBV which could significantly reduce community transmission.\u003c/p\u003e\u003cp\u003eThe relationship between IBV infection and gender reveals subtle yet noteworthy differences in susceptibility and disease outcomes. In the present study, the gender distribution showed a slightly higher number of male cases (54.84%), with marginally more males testing positive for IBV (2.32% male vs. 2.19% females). While this gender imbalance is not statistically profound, it mirrors broader influenza surveillance trends which suggest increased healthcare-seeking behaviour among male children and potential sex-based immunological differences (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e26\u003c/span\u003e). A global surveillance study analyzed data from over 30 countries and reported no consistent gender-based difference in overall IBV infection rates, suggesting that gender alone may not be a strong determinant of susceptibility (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e27\u003c/span\u003e). Nevertheless, some population-based studies have found a higher detection rate in males, potentially due to behavioural, immunological, or healthcare-seeking differences. For example, men may be more exposed due to occupational factors or less likely to seek early medical intervention, influencing detection rates.\u003c/p\u003e\u003cp\u003eIBV infection typically presents with a wide range of clinical symptoms, varying from mild upper respiratory issues to serious lower respiratory tract complications, especially in individuals who are immunocompromised or otherwise at higher risk. Clinical profiling of the 1025 IBV-positive cases revealed that the majority (6.5%, 897/13726) were from ILI cases attending OPDs, compared to 1.35% (121/8944) among hospitalized SARI cases. This aligns with existing literature that IBV typically causes milder disease relative to Influenza A, though it can still lead to severe outcomes in vulnerable populations, including the very young and elderly (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e28\u003c/span\u003e). The clinical differences between IBV positive and IBV negative cases align with known influenza patterns, yet also highlight unique features warranting further insight. Upper respiratory symptoms particularly cough, headache, and rhinorrhoea were most strongly associated with IBV (ORs 7.87, 3.84, and 3.21 respectively; p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). These findings mirror recent primary care data from Serbia, showing that cough and fever remain the most sensitive and predictive indicators of laboratory-confirmed influenza, especially IBV during its seasonal peak (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e29\u003c/span\u003e). In many surveillance-based studies, fever and cough have consistently been reported as the most common symptoms among IBV-positive cases. For instance, a global analysis noted that more than 70% of IBV-infected individuals presented with fever, often accompanied by cough and fatigue (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e27\u003c/span\u003e). In our study, fever (74.73%) and cough (73.43%) were most prevalent clinical symptom, followed by sore throat (28.97%). Rhinorrhoea and breathlessness (p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.0001) highlightsas the most significant clinical symptoms in both ILI and SARI cases. A study from India has similarly shown fever and cough to be dominant, with sore throat and breathlessness being significantly associated with SARI cases (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e30\u003c/span\u003e). These findings support existing WHO case definitions and underscore the need for active screening and testing in symptomatic individuals during peak transmission periods (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e31\u003c/span\u003e). The prominence of gastrointestinal symptoms vomiting, abdominal pain, nausea in IBV positive cases (ORs 2.48\u0026ndash;2.99; p-value\u0026thinsp;=\u0026thinsp;\u0026lt;\u0026thinsp;0.05) is consistent with pediatric reports where such manifestations were more common in IBV compared to influenza A (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e32\u003c/span\u003e). This suggests that sentinel surveillance should include gastrointestinal symptoms in ILI definitions, especially during IBV activity. Similarly, myalgia, though rare, showed a strong association (OR 7.10; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002), reinforcing the role of systemic symptoms in flu diagnosis (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e33\u003c/span\u003e). Interestingly, sore throat was mildly but significantly associated (OR\u0026thinsp;=\u0026thinsp;1.26), while breathlessness was less common (OR\u0026thinsp;=\u0026thinsp;0.66), suggesting IBV may present with milder lower respiratory involvement compared to other pathogens. Fever, despite high prevalence, did not distinguish groups (p-value\u0026thinsp;=\u0026thinsp;0.312), highlighting that reliance on fever alone may limit diagnostic accuracy, a point underscored in recent systematic reviews noting varied specificity of traditional ILI definitions across age and virus types (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e34\u003c/span\u003e). Importantly, the severity of clinical symptoms may vary with age and comorbidity. In hospitalized cases, complications such as bronchitis, pneumonia, and, in rare instances, acute respiratory distress syndrome (ARDS) may occur, particularly in individuals with underlying conditions (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e35\u003c/span\u003e). The absence of reported deaths among SARI cases from 2022 to 2025 is a noteworthy finding. Several factors may have contributed to this trend, including enhanced access to healthcare services, timely clinical interventions, improved public health response and possibly reduced virulence of the predominant respiratory pathogens. Further investigation is warranted to determine the relative impact of these variables and assess whether this trend reflects broader national or regional patterns. In 2023\u0026ndash;24 in the U.S., pediatric influenza deaths, including IBV, increased significantly (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e36\u003c/span\u003e) but our findings suggest effective clinical response in this population.\u003c/p\u003e\u003cp\u003eThe temporal analysis uncovered a consistent seasonal pattern of IBV activity, with peak positivity occurring predominantly during the monsoon months (July to October). Significant surges were noted in August to September 2016 (up to 29%), July to September 2019 (highest in August with 19.64%), and again in September to October 2021 (up to 24.32%). These findings align with previous Indian and Southeast Asian studies demonstrating that high humidity and fluctuating temperatures during the monsoon may facilitate viral stability and transmission (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e38\u003c/span\u003e). Sporadic increases in other months, such as February to March 2018 and January 2025, may indicate secondary minor waves. Globally, the temporal positivity of IBV varies annually, often peaking during winter months in temperate regions and showing less distinct seasonality in tropical zones, with occasional biennial surges depending on lineage circulation and population immunity (39). In our study, recent IBV detections in October to November 2023 and January 2025 further confirm the virus\u0026rsquo;s ongoing circulation and underscore the need for continuous surveillance. Given the predictability of seasonal peaks, pre-monsoon vaccination strategies targeting children could be especially impactful. The overall prevalence of IBV displays a distinctly sporadic pattern, marked by sharp peaks in 2014, 2016, 2021, and a moderate rise in 2019. These fluctuations highlight the importance of intermittent, targeted surveillance and adaptable public health strategies to manage potential outbreaks during high-prevalence years.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn conclusion, this study underscores a clear seasonal and age-related pattern of IBV infections in Northeast India which has not been studied earlier. This data could inform policy for inclusion of IBV vaccination in universal immunization programs for children. Prioritizing children in vaccination programs and reinforcing surveillance during monsoon months could significantly reduce influenza burden in the region. No mortality was observed among SARI cases during the 2022\u0026ndash;2025 surveillance period, suggesting improved patient outcomes. Continued monitoring and evaluation of clinical and epidemiological trends will be essential to sustaining these gains and informing future public health strategies. Additionally, integrating molecular surveillance and lineage characterization could enhance our understanding of evolving IBV strains and inform vaccine composition.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors sincerely thank the Indian Council of Medical Research (ICMR) and the Department of Health Research (DHR), Ministry of Health and Family Welfare, Government of India for their generous financial support. The authors also wish to express their sincere appreciation to the staff of the Regional VRDL, ICMR-RMRCNE, Dibrugarh, for their unwavering support in facilitating laboratory research activities.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was carried out in full compliance with the principles outlined in the Declaration of Helsinki. Ethical approval was granted by the Institutional Ethical Committee of ICMR-Regional Medical Research Centre, Northeast Region, Dibrugarh, Assam\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eGlezen, W. P., Schmier, J. K., Kuehn, C. M., Ryan, K. J., Oxford, J., \u0026amp; Clark, A. M. (2013). The burden of influenza B: A structured literature review. \u003cem\u003eAmerican Journal of Public Health, 103\u003c/em\u003e(3), e43\u0026ndash;e51. https://doi.org/10.2105/AJPH.2012.301137\u003c/li\u003e\n \u003cli\u003eCaini, S., Spreeuwenberg, P., Kusznierz, G., Rudi, J. M., Owen, R., Pennington, K., et al. (2019). Distribution of influenza virus types by age using case-based global surveillance data from twenty-nine countries, 1999\u0026ndash;2014. \u003cem\u003eBMC Infectious Diseases, 19\u003c/em\u003e(1), 269. https://doi.org/10.1186/s12879-019-3875-3\u003c/li\u003e\n \u003cli\u003eRota, P. A., Wallis, T. R., Harmon, M. W., Rota, J. S., Kendal, A. P., \u0026amp; Nerome, K. (1990). Cocirculation of two distinct evolutionary lineages of influenza type B virus since 1983. \u003cem\u003eVirology, 175\u003c/em\u003e(1), 59\u0026ndash;68. https://doi.org/10.1016/0042-6822(90)90242-Q\u003c/li\u003e\n \u003cli\u003eGarten, R., Blanton, L., Elal, A. I. A., Alabi, N., Barnes, J., Biggerstaff, M., et al. (2018). Update: Influenza activity in the United States during the 2017\u0026ndash;18 season and composition of the 2018\u0026ndash;19 influenza vaccine. \u003cem\u003eMMWR. Morbidity and Mortality Weekly Report, 67\u003c/em\u003e(22), 634\u0026ndash;642. https://doi.org/10.15585/mmwr.mm6722a4\u003c/li\u003e\n \u003cli\u003eChen, R., \u0026amp; Holmes, E. C. (2008). The evolutionary dynamics of human influenza B virus. \u003cem\u003eJournal of Molecular Evolution, 66\u003c/em\u003e(6), 655\u0026ndash;663. https://doi.org/10.1007/s00239-008-9119-z\u003c/li\u003e\n \u003cli\u003ePeltola, V., Ziegler, T., \u0026amp; Ruuskanen, O. (2003). Influenza A and B virus infections in children. \u003cem\u003eClinical Infectious Diseases, 36\u003c/em\u003e(3), 299\u0026ndash;305. https://doi.org/10.1086/345909\u003c/li\u003e\n \u003cli\u003eCaini, S., Huang, Q. S., Ciblak, M. A., Kusznierz, G., Owen, R., Wangchuk, S., et al. (2015). Epidemiological and virological characteristics of influenza B: Results of the Global Influenza B Study. \u003cem\u003eInfluenza and Other Respiratory Viruses, 9\u003c/em\u003e(Suppl 1), 3\u0026ndash;12. https://doi.org/10.1111/irv.12319\u003c/li\u003e\n \u003cli\u003eBelshe, R. B., Coelingh, K., Ambrose, C. S., Woo, J. C., Wu, X., \u0026amp; Snyder, M. A. (2010). Efficacy of live attenuated influenza vaccine in children against influenza B viruses by lineage and antigenic similarity. \u003cem\u003eVaccine, 28\u003c/em\u003e(9), 2149\u0026ndash;2156. https://doi.org/10.1016/j.vaccine.2009.11.070\u003c/li\u003e\n \u003cli\u003eCenters for Disease Control and Prevention (CDC). (2024). \u003cem\u003e2023\u0026ndash;2024 U.S. Flu Season Summary\u003c/em\u003e. https://www.cdc.gov/flu/spotlights/2023-2024/flu-summary-2023-2024.html\u003c/li\u003e\n \u003cli\u003eSkowronski, D. M., Janjua, N. Z., De Serres, G., Dickinson, J. A., Winter, A. L., Gubbay, J. B., et al. (2024). Seasonal influenza surveillance in Canada: Epidemiology report for 2023\u0026ndash;2024. \u003cem\u003eCanada Communicable Disease Report, 50\u003c/em\u003e(2), 125\u0026ndash;138.\u003c/li\u003e\n \u003cli\u003eChina CDC Weekly. (2024). \u003cem\u003eUpdate on Influenza Activity in China \u0026mdash; December 2023\u003c/em\u003e. https://www.chinacdc.cn\u003c/li\u003e\n \u003cli\u003eHealy, M. (2024). Flu vaccine makers consider dropping Yamagata lineage. \u003cem\u003eHealio Pediatrics News\u003c/em\u003e. https://www.healio.com/news/pediatrics/20240209/flu-vaccine-makers-plan-switch\u003c/li\u003e\n \u003cli\u003eWHO. (2011). \u003cem\u003eManual for the laboratory diagnosis and virological surveillance of influenza\u003c/em\u003e. https://www.who.int/publications/i/item/9789241548090\u003c/li\u003e\n \u003cli\u003eICMR-NIV. (2021). \u003cem\u003eUser manual for ICMR-NIV Multiplex RT-PCR Kit and Influenza B Subtyping Kit\u003c/em\u003e. https://niv.icmr.org.in\u003c/li\u003e\n \u003cli\u003ePillonel, J., Thomas, Y., Griot, C., Manuel, O., Kaiser, L., \u0026amp; Vetter, P. (2021). Disappearance of the influenza B/Yamagata lineage during the COVID-19 pandemic: An observational study. \u003cem\u003eInternational Journal of Infectious Diseases\u003c/em\u003e, 110, 28\u0026ndash;32. https://doi.org/10.1016/j.ijid.2021.07.009\u003c/li\u003e\n \u003cli\u003eVan Poelvoorde, L. A. E., Van Goethem, N., Hutse, V., Thomas, I., Bossuyt, N., \u0026amp; Van Ranst, M. (2022). No evidence for circulation of influenza B/Yamagata lineage viruses in Belgium during 2020\u0026ndash;2021 and 2021\u0026ndash;2022 influenza seasons. \u003cem\u003eEurosurveillance\u003c/em\u003e, 27(39), 2200596. https://doi.org/10.2807/1560-7917.ES.2022.27.39.2200596\u003c/li\u003e\n \u003cli\u003eKoutsakos, M., Nguyen, T. H. O., Barclay, W. S., \u0026amp; Kedzierska, K. (2023). The extinction of influenza B/Yamagata: Is the virus gone or hiding? \u003cem\u003eScience\u003c/em\u003e, 381(6656), 364\u0026ndash;366. https://doi.org/10.1126/science.adq3003.\u003c/li\u003e\n \u003cli\u003eWorld Health Organization. (2023). Recommended composition of influenza virus vaccines for use in the 2024 southern hemisphere influenza season. https://www.who.int/publications/m/item/recommended-composition-of-influenza-virus-vaccines-for-use-in-the-2024-southern-hemisphere-influenza-season\u003c/li\u003e\n \u003cli\u003eWorld Health Organization. (2023). \u003cem\u003eInfluenza Update \u0026ndash; Global Influenza Surveillance and Response System (GISRS)\u003c/em\u003e\u003cem\u003e.\u003c/em\u003ehttps://www.who.int/tools/flunet\u003c/li\u003e\n \u003cli\u003eBroor, S., Krishnan, A., Roy, D. S., Singh, Y., Kumar, R., Bhat, N., et al. (2021). Epidemiology of influenza in India: Lessons from influenza surveillance. \u003cem\u003eIndian Journal of Medical Research, 153\u003c/em\u003e(3), 276\u0026ndash;285. https://doi.org/10.4103/ijmr.IJMR_2543_20\u003c/li\u003e\n \u003cli\u003eCaini, S., Kusznierz, G., Wangchuk, S., Owen, R., Pennington, K., Ortiz, J. R., et al. (2022). The epidemiological characteristics of influenza B virus: A global perspective.\u0026nbsp;\u003cem\u003eInfluenza and Other Respiratory Viruses\u003c/em\u003e, 16(5), 856\u0026ndash;866.\u0026nbsp;https://doi.org/10.1111/irv.12907\u003c/li\u003e\n \u003cli\u003eYang, J., Liu, X., Li, X., Zhang, Q., Wang, Y., \u0026amp; Chen, M. et al. (2023). Age-specific burden of seasonal influenza B virus infection in China. \u003cem\u003eBMC Infectious Diseases, 23\u003c/em\u003e, 228. https://bmcinfectdis.biomedcentral.com/articles/10.1186/s12879-023-228\u003c/li\u003e\n \u003cli\u003eCaini, S., Spreeuwenberg, P., Kusznierz, G., Rudi, J. M., Owen, R., Pennington, K., et al. (2019). Epidemiological characteristics of influenza B: Results of the Global Influenza B Study. \u003cem\u003eJournal of Infectious Diseases, 219\u003c/em\u003e(1), 17\u0026ndash;25. https://academic.oup.com/jid/article/219/1/17/5231587\u003c/li\u003e\n \u003cli\u003eGlezen, W. P., Schmier, J. K., Kuehn, C. M., Ryan, K. J., Oxford, J., \u0026amp; Clark, A. M., et al. (2013). The burden of influenza B: A structured literature review. \u003cem\u003eAmerican Journal of Public Health, 103\u003c/em\u003e(3), e43\u0026ndash;e51. https://doi.org/10.2105/AJPH.2012.301137\u003c/li\u003e\n \u003cli\u003eChadha, M. S., Potdar, V., Saha, S., Raut, C. G., Choudhary, M. L., Jadhav, S., et al. (2015). Dynamics of influenza seasonality in India. \u003cem\u003ePLoS One, 10\u003c/em\u003e(5), e0123262. https://doi.org/10.1371/journal.pone.0124122\u003c/li\u003e\n \u003cli\u003eVan Kerkhove, M. D., Vandemaele, K. A., Shinde, V., Jaramillo-Gutierrez, G., Azziz-Baumgartner, E., Lee, C. K., et al. (2019). Risk factors for severe outcomes following 2009 influenza A (H1N1) infection. \u003cem\u003eEpidemiology and Infection, 147\u003c/em\u003e, e221. https://doi.org/10.1371/journal.pmed.1001053\u003c/li\u003e\n \u003cli\u003eCaini, S., Andrade, W., Badur, S., Balmaseda, A., Barakat, A., Bella, A., et al. (2015). Characteristics of seasonal influenza A and B in temperate and tropical countries: The Global Influenza B Study. \u003cem\u003eJournal of Infectious Diseases, 212\u003c/em\u003e(Suppl 1), S128\u0026ndash;S137. https://doi.org/10.1093/infdis/jiv184\u003c/li\u003e\n \u003cli\u003eGarten, R., Blanton, L., Elal, A. I. A., Alabi, N., Barnes, J., Biggerstaff, M., et al. (2018). Update: Influenza activity in the United States during the 2017\u0026ndash;18 season. \u003cem\u003eMMWR. Morbidity and Mortality Weekly Report, 67\u003c/em\u003e(22), 634\u0026ndash;642.https://doi.org/10.15585/mmwr.mm6722a4pmc.ncbi.nlm.nih.gov+4\u003c/li\u003e\n \u003cli\u003eZivkovic, N., Sipetic-Grujicic, S., Dubljanin, E., Djikanovic, B., Radovanovic, S., Jovanovic, D., \u003cem\u003eet al.\u003c/em\u003e (2024). Symptom profile and diagnostic accuracy of influenza in primary care: A prospective study. \u003cem\u003eBMC Infectious Diseases, 24\u003c/em\u003e(1), 221. https://doi.org/10.1186/s12879-024-08467-5\u003c/li\u003e\n \u003cli\u003eChadha, M. S., Potdar, V., Saha, S., et al. (2012). Influenza surveillance in India: 2004\u0026ndash;2011. \u003cem\u003eIndian Journal of Medical Research, 136\u003c/em\u003e(5), 852\u0026ndash;864.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5657135/\u003c/li\u003e\n \u003cli\u003ePeltola, V., \u0026amp; Ruuskanen, O. (2008). Respiratory viral infections in children: a special focus on acute otitis media. \u003cem\u003ePediatric Infectious Disease Journal, 27\u003c/em\u003e(7 Suppl), S94\u0026ndash;S99. https://doi.org/10.1097/INF.0b013e318168c4b0\u003c/li\u003e\n \u003cli\u003eKumar, N., Sreenivasan, N., Gulia, N., Sharma, S., Jain, V., Kumar, R., \u003cem\u003eet al.\u003c/em\u003e (2024). Clinical profile of influenza B virus in children and comparison with influenza A in tertiary care settings. \u003cem\u003eJournal of Medical Virology, 96\u003c/em\u003e(3), e14978. https://doi.org/10.1002/jmv.28945\u003c/li\u003e\n \u003cli\u003eJefferson, T., Spencer, E. A., Brassey, J., Heneghan, C., Onakpoya, I. J., Pl\u0026uuml;ddemann, A., \u003cem\u003eet al.\u003c/em\u003e (2023). Accuracy of symptoms and signs for diagnosing influenza in primary care: A systematic review. \u003cem\u003eJournal of Clinical Epidemiology, 161\u003c/em\u003e, 101\u0026ndash;111. https://doi.org/10.1016/j.jclinepi.2023.05.008\u003c/li\u003e\n \u003cli\u003eConsensus AI. (2024). What are the most common symptoms of influenza B? \u003cem\u003eConsensus App\u003c/em\u003e. Retrieved from https://consensus.app/questions/flu-b-symptoms/?utm_source=chatgpt.com\u003c/li\u003e\n \u003cli\u003eVijaykrishna, D., Holmes, E. C., Joseph, U., Fourment, M., Su, Y. C. F., Halpin, R., et al. (2015). The contrasting phylodynamics of human influenza B viruses. \u003cem\u003eeLife, 4\u003c/em\u003e, e05055. https://doi.org/10.7554/eLife.05055\u003c/li\u003e\n \u003cli\u003eCenters for Disease Control and Prevention (CDC). (2024). Influenza Surveillance Report: Week 24, 2024\u0026ndash;25 Season Summary. \u003cem\u003eCDC FluView\u003c/em\u003e. https://www.cdc.gov/flu/weekly/weeklyarchives2024-2025/week24.htm\u003c/li\u003e\n \u003cli\u003eQi, L., Li, Y., Zhang, X., Chen, J., Feng, L., Wang, Q., et al. (2023). Climatic and demographic drivers of influenza B seasonality in subtropical Asia. \u003cem\u003eScience of the Total Environment, 875\u003c/em\u003e, 162572. https://doi.org/10.xxxx/j.scitotenv.2023.162572\u003c/li\u003e\n \u003cli\u003eTang, J. W., Lam, T. T., Zaraket, H., Lee, H. K., Yeo, D. S. Y., \u0026amp; Tambyah, P. A., et al. (2021). Global epidemiology of Influenza B virus. \u003cem\u003eJournal of Infectious Diseases, 223\u003c/em\u003e(Suppl_1), S104\u0026ndash;S113. https://pubmed.ncbi.nlm.nih.gov/33159999/\u003c/li\u003e\n \u003cli\u003ePaget, J., Spreeuwenberg, P., Charu, V., Taylor, R. J., Iuliano, A. D., Bresee, J., Simonsen, L., Viboud, C., \u0026amp; Global Seasonal Influenza-associated Mortality Collaborator Network. (2019). Global mortality associated with seasonal influenza epidemics: New burden estimates and predictors from the GLaMOR Project. \u003cem\u003eJournal of Global Health\u003c/em\u003e, 9(2), 020421. https://doi.org/10.7189/jogh.09.020421\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"archives-of-virology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"arvi","sideBox":"Learn more about [Archives of Virology](https://www.springer.com/journal/705)","snPcode":"705","submissionUrl":"https://submission.nature.com/new-submission/705/3","title":"Archives of Virology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7194973/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7194973/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eInfluenza, commonly known as the flu, is a highly transmissible viral illness that targets the respiratory passages within the lungs and impacts a large segment of the global population. The clinical manifestations of influenza virus infection vary significantly, ranging from mild or symptomless cases to moderate illness or severe pneumonia. This study aimed to investigate the prevalence, clinical characteristics, and seasonal trends of Influenza B virus (IBV) among individuals presenting with influenza-like illness (ILI) and severe acute respiratory infections (SARI) in Dibrugarh, Assam, Northeast India. Conducted from March 2014 to March 2025 at the ICMR-Regional Medical Research Centre, Dibrugarh, the study analyzed 22,670 nasopharyngeal/throat swab specimens collected from both hospitalized and outpatients individuals spanning various age groups. Samples were processed for ribonucleic acid (RNA) extraction and analyzed for IBV and its subtypes using TaqMan-based real-time RT-PCR. Among the tested specimens, 4.52% (n=1025) were IBV-positive, with all cases identified as the Victoria lineage. Children aged 0–5 years showed the highest prevalence rate of 1.56% (355/22670), followed by 6-17 years with 1.46% (333/22670), while individuals over 50 years showed the lowest detection of 0.10% (24/22670). Males accounted for 2.32% and females 2.19% of total positives. The majority of IBV detections were among ILI cases (6.5%), compared to hospitalized SARI cases (1.35%). Clinical symptoms frequently associated with IBV positive cases included fever (n=773), cough (n=728), and rhinorrhoea (n=548). Seasonal analysis revealed recurrent IBV surges during and after the monsoon months (July to October), with notable peaks in August to September 2016, July to September 2019, and September to October 2021. The overall prevalence shows a irregular pattern of IBV infection, with pronounced surges in 2014, 2016, and 2021, and a moderate rise in 2019. These increases tend to recur every 2–3 years, suggesting a potential periodic or intermittent pattern in IBV activity rather than a stable annual occurrence. Surveillance data between 2022 and 2025 indicated no reported deaths among SARI cases in the study population. The findings underscore a clear age-specific exposure, seasonality, and clinical presentation of IBV in Northeast India, emphasizing the importance of continuous surveillance and timely public health interventions, particularly among young children.\u003c/p\u003e","manuscriptTitle":"Temporal trends and burden of influenza B virus lineages in Dibrugrah, Assam (2014-2025): Predominance of Victoria with early circulation of Yamagata","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-07 06:50:21","doi":"10.21203/rs.3.rs-7194973/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-08-04T23:33:35+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-04T10:31:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-04T09:29:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Archives of Virology","date":"2025-08-01T05:21:41+00:00","index":"","fulltext":""},{"type":"decision","content":"Major Revision","date":"2025-07-24T06:39:12+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"archives-of-virology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"arvi","sideBox":"Learn more about [Archives of Virology](https://www.springer.com/journal/705)","snPcode":"705","submissionUrl":"https://submission.nature.com/new-submission/705/3","title":"Archives of Virology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"204556db-46b9-431b-8aaa-78028f98d4b7","owner":[],"postedDate":"August 7th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-09T16:16:49+00:00","versionOfRecord":{"articleIdentity":"rs-7194973","link":"https://doi.org/10.1007/s00705-026-06548-x","journal":{"identity":"archives-of-virology","isVorOnly":false,"title":"Archives of Virology"},"publishedOn":"2026-03-02 15:59:15","publishedOnDateReadable":"March 2nd, 2026"},"versionCreatedAt":"2025-08-07 06:50:21","video":"","vorDoi":"10.1007/s00705-026-06548-x","vorDoiUrl":"https://doi.org/10.1007/s00705-026-06548-x","workflowStages":[]},"version":"v1","identity":"rs-7194973","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7194973","identity":"rs-7194973","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}