COVID-19 disruption and rebound of respiratory syncytial virus hospital burden in Australia: A national interrupted time-series analysis.

BackgroundCOVID-19 non-pharmaceutical interventions disrupted respiratory syncytial virus (RSV) transmission globally. In Australia, RSV surged back after restrictions eased, whether this reflected immunity debt repayment or epidemic amplification is untested.MethodsWe conducted a national interrupted time-series analysis using Australian Institute of Health and Welfare hospitalisation data from financial years (FY) 2010/11-2023/24. The primary outcome was RSV-attributable fraction (RSV-AF) of bronchiolitis in infants and children 1-4 years. Pre-pandemic counterfactual trends were estimated by linear extrapolation of FY2010/11-2019/20 training data, this was appropriate given the stable, low-gradient pre-pandemic RSV-AF trends in both groups. For adults ≥ 65 years, a flat counterfactual (pre-pandemic mean) to bound estimates where a secular ascertainment rise made linear extrapolation inappropriate. Formal amplification test: one-sided Z-test of whether rebound exceeded suppression deficit. Influenza-attributable fraction used as a pathogen-specific comparator to isolate RSV from general respiratory rebound. Non-RSV bronchiolitis decomposed to rule out general post-pandemic denominator effects.ResultsIn infants, pre-pandemic RSV-AF was 32.3% (SD 1.8%). In FY 2022/23, it reached 52.0% (z = 10.78; p