This retrospective, descriptive population-based study evaluated the seasonal dynamics and burden of respiratory syncytial virus (RSV), influenza, and COVID-19 reported through Brazil’s national severe acute respiratory infection surveillance system (SIVEP) between 2019 and 2023. The primary aim was to characterise epidemiological patterns to inform timing of preventive interventions including seasonal vaccination and preparedness strategies.
The investigation used national surveillance data collected in SIVEP. The authors analysed laboratory-confirmed SARI cases attributed to RSV, influenza, and COVID-19 across the 2019–2023 study period. They examined confirmed cases, hospitalisations, and deaths for each pathogen.
Time-series decomposition and seasonal trend analysis were performed using the multiple seasonal-trend decomposition via locally estimated scatterplot smoothing method. Monthly mean values for each aetiology were calculated to assess and quantify seasonal burden.
Among laboratory-confirmed SARI cases reported in SIVEP during the study period there were: 69,389 RSV cases, 45,881 influenza cases, and 2,299,712 COVID-19 cases. Age distributions varied substantially by pathogen. More than 90% of RSV diagnoses were reported in children aged 0–10 years, while influenza and COVID-19 were more commonly reported among older adults.
A notable temporal change in paediatric mortality attributed to RSV was reported: the proportion of deaths in children related to RSV increased from 19.2% in 2020 to 62.0% in 2023. The source reports these shifts within the surveillance data but does not provide detailed breakdowns of absolute death counts in the abstract.
Seasonal peaks differed by pathogen. RSV seasonal peaks typically occurred from March to June. Influenza case counts peaked in January. COVID-19 did not demonstrate a consistent seasonal pattern over the study period and showed more variable timing of peaks.
Geographic variation was observed across Brazil, with higher concentrations of reported cases in the Southeast and South regions. The source indicates regional differences in case distribution but does not present full regional incidence rates in the abstract.
The authors emphasise that observed burden and seasonality may be influenced by variations in testing strategies over time and across regions. They specifically highlight the likelihood of underreporting for adult RSV cases, attributable to limited testing and reduced diagnostic sensitivity. Where testing is reduced or selective, surveillance case counts and apparent seasonality can be biased.
The surveillance-based nature of the analysis means findings reflect the population captured by SIVEP and laboratory-confirmation practices, rather than the entire burden of disease in the community. The abstract does not provide sensitivity analyses or alternative data sources beyond the SIVEP system.
Based on the described patterns, the authors recommend strengthening diagnostic capacity and surveillance, particularly to better capture adult RSV. They affirm the continued importance of seasonal vaccination programmes such as influenza vaccination and suggest potential enhancements through integration of new preventive measures. These measures explicitly mentioned in the source include RSV vaccination for older adults and maternal immunisation to protect infants.
Timing of vaccination and preventive interventions should consider the pathogen-specific seasonality reported here—for example, influenza peaks in January and RSV peaks from March to June—while also accounting for local and regional variation and potential yearly shifts in circulation.
This observational study was published in J Glob Health. Authors were affiliated with Pfizer (São Paulo and New York) and IQVIA (São Paulo). The abstract includes a conflict of interest statement noting that several authors were employees of Pfizer and that the IQVIA authors conducted analyses with stated autonomy. The source provides the PMID and DOI for the full report for readers who require detailed methods, regional breakdowns, or full results beyond the abstract.
Note: All statements above are drawn from the source abstract and accompanying metadata. The abstract does not report some granular details (for example, absolute death counts by year, stratified regional incidence rates, or complete testing strategy timelines), and those specifics were not reported in the source abstract.