Six-year epidemiological dynamics of human respiratory syncytial virus infections in children in central China (2019-2024): pandemic suppression, 2023 resurgence, and immune debt effect

Background: Human respiratory syncytial virus (HRSV) is a leading cause of acute respiratory infections in children. COVID-19 NPIs significantly suppressed HRSV transmission. This study analyzed six-year epidemiological dynamics of pediatric HRSV infections in Henan Province, China, focusing on NPI suppression effects, the 2023 resurgence, and "Immune debt" impact. Methods: We retrospectively collected respiratory specimens from 80,920 children with acute respiratory diseases at Henan Children's Hospital (2019-2024). HRSV was detected using RT-qPCR. Positivity rates were analyzed by year, season, and age group. Results: During 2019-2024, HRSV positivity fluctuated markedly: 14.65% (2019), 16.34% (2021), 3.27% (2022 under strict NPIs), 21.47% (2023 post-NPIs), and 6.80% (2024). Interrupted time-series analysis indicated that NPI lifting in 2023 was associated with a significant surge in infection risk (OR = 668.77, 95% CI: 47.03-9509.28). Seasonal patterns shifted substantially, with the characteristic winter peak replaced by an off-season spring outbreak in April 2023 (57.41%). Multivariable logistic regression identified age as the strongest predictor, with infants <1 year having the highest risk (aOR = 9.02, 95% CI: 8.31-9.79) and a 4.91-fold higher positivity rate than school-aged children (22.98% vs. 4.68%; 95% CI: 4.59-5.25; P < 0.001). Conclusions: NPIs dramatically affected HRSV epidemiology. The intense post-suppression rebound strongly supports the "Immune debt" theory-accumulation of susceptible children driving resurgence. Establishing year-round, multi-pathogen surveillance systems is crucial for post-pandemic public health challenges.