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

IntroductionRespiratory 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. MethodsWe 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. ResultsReported 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. ConclusionsStable 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 MessagesO_LIWhat is already known on this topic: RSV is an important driver of acute lower respiratory tract infections, which represent the leading cause of mortality in children under five across the globe. RSV demonstrates highly seasonal dynamics, as its transmission is linked to climate. C_LIO_LIWhat this study adds: We quantified correlates of RSV infection and estimated the seasonal transmission rate for RSV from reported patient data in Antananarivo, Madagascar. We found that RSV transmission is primarily concentrated in very young children ([≤]1 year) in Antananarivo and positively associated with high precipitation and low humidity, which focus most transmission in Madagascars January-February rainy season. C_LIO_LIHow this study might affect research, practice, or policy: Our study suggests that RSV burden may intensify with future climate change, particularly higher rainfall. We emphasize the high public health importance of accelerating the introduction of recently-developed mAbs (Monoclonal Antibody) and vaccination interventions to combat RSV to low-income settings like Madagascar. C_LI