Pediatric acute respiratory virus hospitalizations: a population-based cohort study, 2017-2024

Background and objectives — COVID-19 mitigation measures resulted in widespread disruptions to seasonal respiratory viruses. The objective of this study was to compare observed and expected pediatric viral acute respiratory infection (ARI) related hospitalizations, and the characteristics of admitted children, post-pandemic onset.

Methods — Total and virus-specific ARI-related hospitalization rates were determined using a population-based cohort of all youth <18 years in Ontario, Canada between July 1, 2017 and June 30, 2024. Sociodemographic and clinical characteristics were identified from linked administrative data. Expected weekly post-pandemic age-and-sex-specific admission rates were estimated using Poisson regression; adjusted rate ratios (RRs) and 95% confidence intervals (CIs) were reported.

Results — This cohort included ∼2.7 million youth per year. There was a sharp reduction in ARIs in 2020/21, followed by a moderate return in 2021/22; however, influenza remained mostly absent (n=168). 2022/23 was marked by an out-of-season persistence and overwhelming ARI burden, particularly for RSV (n=4,701 admissions versus 1,969-2,357 pre-pandemic) and human metapneumovirus (n=377 versus 93-127). Overall, more older children (mean age: 38.9-42.8 versus 37.2-37.9 months pre-pandemic) and fewer males were admitted post-pandemic for ARIs; males were the only group with lower-than-expected 2022/23 admissions (RR:0.64, 95%CI: 0.59-0.71 for all ARIs). COVID-19-related admissions contributed minimally to ARI-related hospitalizations overall, particularly among <5-year-olds. Pre-pandemic seasonality appears to nearly have resumed in 2023/24.

Conclusions — Post-pandemic disruptions in multiple viral ARIs substantially influenced the intensity, timing, and characteristics of children seeking healthcare. Although 2023/24 was more typical, it is not yet clear when – or if – pre-pandemic ARI seasonality and epidemiology will resume.