Age redistribution and altered RSV seasonality in Taiwan: A multicenter analysis from 2015 to 2023

OBJECTIVES: Respiratory syncytial virus (RSV) is a major cause of pediatric pneumonia. In this study, we assessed RSV epidemiology in Taiwan and explored potential changes in respiratory pathogen dynamics. METHODS: We analyzed respiratory pathogen data from medical centers in Taiwan between 2015 and 2023. We also examined Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis cases to assess potential shifts in respiratory bacterial trends and age distributions. RESULTS: A total of 7,098 RSV cases were identified. Before 2020, RSV circulated year-round, peaking from July to September. After 2020, RSV activity shifted to a sharply increased epidemic from September to December and became more synchronized nationwide. The percentage of infants (2 years diagnosed with RSV increased significantly (P < 0.001). Concomitant increases in bacterial detection were observed among older children, particularly for S. pneumoniae and H. influenzae, suggesting possible viral-bacterial interactions. CONCLUSION: The shift in age distribution and increased bacterial codetections highlight the need for ongoing RSV surveillance. Given the unpredictability of RSV seasonality, both maternal immunization and monoclonal antibody administration may offer reliable protection for infants.