Climatic drivers of seasonal dynamics for Respiratory Syncytial Virus (RSV) in Antananarivo, Madagascar, 2011-2021

Introduction Respiratory Syncytial Virus (RSV) is a primary source of acute lower respiratory tract infection (ALRTI), the leading cause of death in children under five. Over 99% of RSV-attributed deaths occur in low-income countries, including Madagascar. RSV transmission is linked to climate, driving highly seasonal dynamics. Methods We used generalized additive models (GAMs) to identify correlates of reported RSV infections in Antananarivo, Madagascar from January 2011-December 2021, then fit catalytic models to cumulative age-structured incidence to estimate age-specific force of infection (FOI). We fit a time series Susceptible-Infected-Recovered (TSIR) model to the dataset to estimate weekly RSV transmission, then evaluated associations with precipitation, humidity, and temperature using generalized linear models. We used GAMs to quantify interannual trends in climate and assess whether significant deviations in RSV burden occurred in years representing climatic anomalies. Results Reported RSV infections in Antananarivo were significantly associated with patient ages ≤2 years. Highest FOI was estimated in patients ≤1 year, with transmission declining to near-zero by age five before rising in older (60+) cohorts. TSIR models estimated a January–February peak in RSV transmission, which was strongly positively associated with precipitation and more weakly with temperature but negatively related to relative humidity. Precipitation, humidity, and temperature all increased across the study period in Antananarivo, while reported RSV infections remained stable. Significant deviations in RSV burden were not associated with clear climate anomalies. Conclusions Stable rates of reported RSV infections in Antananarivo across the past decade may reflect contrasting impacts of elevated precipitation and increased humidity on transmission. If future climate changes yield more rapidly accelerating precipitation than humidity, this could accelerate RSV burden. Introduction of recently-developed public health interventions to combat RSV in low-income settings like Madagascar is essential to mitigating burden of disease (RSV), in particular any future climate-driven increases in transmission or severity. Key Messages ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research was supported by the US Centers for Disease Control and Prevention (Cooperative Agreement to JMH: NU51IP000812), the Bill and Melinda Gates Foundation (grant awards to CEB: OPP 1211841 and INV 049262), and the National Geographic Society Coding for Conservation program (grant award to CEB: 102825). The funders had no role in the study design, data collection or analysis, the decision to publish, or preparation of the manuscript. ### 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: Ethics committee of the Ministry of Health of Madagascar gave ethical approval for this work 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 All data produced in the present study are available upon reasonable request to the authors