Delayed seasonality but consistent age burden: RSV epidemiology pre-, during and post-COVID-19 pandemic on the Kenyan Coast (2008-2026)

Abstract Background The COVID-19 pandemic and associated non-pharmaceutical interventions disrupted the established epidemiological patterns of many endemic respiratory viruses globally. However, its impact on respiratory syncytial virus (RSV) epidemiology in sub-Saharan Africa is understudied. Methods We analyzed data from a continuous hospital-based pediatric pneumonia surveillance program in coastal Kenya from January 2008-June 2026. Children ≤5 years, admitted with WHO-defined syndromic severe or very severe pneumonia were tested for RSV using quantitative RT-PCR. The period was stratified into pre-pandemic (January 2008-March 2020), during-pandemic (March 2020-May 2023) and post-pandemic (May 2023-June 2026). Multivariable logistic regression evaluated clinical and demographic shifts across periods. Results Among 10,374 tested children, 2,442 (23.5%) were RSV-positive. Positivity declined from 25.3% (1,919/7,585) pre-pandemic to 18.3% (235/1,282) during the pandemic and 19.1% (288/1,507) post-pandemic. Overall median age of RSV-positive patients remained statistically consistent across all periods (4.3 vs 3.7 vs 3.1 months; p=0.108), with ≤6-month-olds accounting for ∼62% of admissions throughout. However, in the 2020/21 season RSV-positive children had increased median age (6.7, IQR: 2.0-15.1 months). In multivariable analysis, fever was less frequent during and post-pandemic (adjusted p< 0.001), and cough decreased post-pandemic (adjusted p=0.002). Pneumonia severity and overall mortality did not significantly differ across the periods. Local RSV season onsets exhibited 1-2 months delay during and post-pandemic compared to pre-pandemic. Conclusions Despite a repeated 1–2-month delay of RSV season onsets on the Kenyan coast and minor clinical symptoms shifts, the core demographic patterns remained stable. The persisting severe RSV disease in <6-month-olds highlights this population for RSV interventions.