# 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

## TL;DR

This study tracks how HRSV infections in children in central China changed over six years, showing a big increase after pandemic restrictions were lifted due to immune debt.

## Contribution

The study provides empirical evidence supporting the 'immune debt' theory through detailed HRSV epidemiological data in post-pandemic China.

## Key findings

- HRSV positivity surged to 21.47% in 2023 after NPIs were lifted, with a strong odds ratio of 668.77.
- Infants under one year had a 9.02-fold higher risk of HRSV infection compared to older children.
- The 2023 outbreak occurred in spring, breaking the typical winter season pattern.

## Abstract

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.

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.

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).

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.