Earlier and prolonged respiratory syncytial virus (RSV) seasons in young children compared to adults: implications for prevention in infants.

Respiratory syncytial virus (RSV) poses a major health concern, particularly for young children and older adults. In this 10-year, single-center retrospective study (15 May 2015 to 14 May 2025), we analyzed RSV positivity rates to characterize local epidemiologic trends. When stratified by age, children ≤2 years consistently exhibited the highest positivity rates. Using the Centers for Disease Control and Prevention's 3% positivity threshold, we found that the RSV season in the general population in our region began in early July and ended in late December, approximately 3 months earlier than the national average. Among infants ≤2 years, the season lasted 5 weeks longer on average than in the general population. These findings highlight regional variability in RSV seasonality and the earlier onset and extended duration of RSV activity in young children. This age group appeared particularly susceptible and likely played a key role in initiating and sustaining community transmission. Monitoring RSV positivity specifically in children ≤2 years, separate from the general population, may enhance local surveillance accuracy and support more timely decisions regarding RSV immunoprophylaxis and vaccination strategies.

Importance: Respiratory syncytial virus (RSV) is a major health concern, especially for young children and older adults. In this study, we explored whether different age groups changed the timing of RSV season. This is important because public health guidelines, hospital preparedness, and preventive strategies like antibody prophylaxis and vaccination rely on accurate RSV season timing. By showing how RSV trends differ by age, our findings can help improve seasonality responses and ensure that preventive measures reach high-risk groups, especially infants, at the right time.