Sustained impact of 10-valent pneumococcal conjugate vaccine on invasive pneumococcal disease in Kenya, 2011-2022

Background There are only a few long-term PCV impact assessments in sub-Saharan Africa, and these have been confined to settings using a 13-valent PCV. A 10-valent PCV was introduced in Kenya in 2011 with catchup vaccination among children aged <5 years in Kilifi. We evaluated the impact of PCV10 introduction in Kilifi through 2022.

Surveillance for IPD among residents of the Kilifi Health and Demographic Surveillance System was conducted at the Kilifi County Referral Hospital. Identification of pneumococcus isolated from blood or cerebrospinal fluid and pneumococcal serotyping were conducted according to WHO recommendations. Age– and serotype-specific incidence rate ratios, adjusted for pre-defined confounders (aIRRs), were used to compare annual IPD incidence in the pre-vaccine period to that in 2017-2019 (late post-vaccine) and 2020-2022 (COVID-19). Findings Compared to the pre-vaccine period, the incidence of vaccine serotype (VT) IPD among children aged <5 years was significantly lower in 2017-2019 (aIRR 0.14; 95%CI 0.04-0.49) and in 2020-2022 (aIRR 0.03; 95%CI 0.00-0.25). It also declined among older children and adults. The incidence of non-VT (NVT) IPD among children aged <15 years was higher during the post-vaccine period. All serotype IPD incidence declined across all age groups. Among individuals with NVT-IPD, serotypes included in new-generation PCVs accounted for about one-third and about one-half of disease among individuals aged <5 years and ≥5 years, respectively. Interpretation Despite potential waning of the effects of catchup vaccination during introduction, reductions in VT-IPD incidence were sustained through 12 years of PCV10 use. All serotype IPD incidence declined across all ages despite serotype replacement among children. New-generation PCVs may enhance IPD control. Competing Interest Statement The authors have declared no competing interest. Funding Statement Gavi, The Vaccine Alliance. EWK was funded by the Foreign Commonwealth & Development Office and the Bill & Melinda Gates Foundation Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval to conduct the study was granted by Kenya Medical Research Institute Scientific Ethics Review Unit (SSC 1433) and the Oxford Tropical Research Ethics Committee (30-10). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability All data produced in the present study are available upon reasonable request to the authors.