Background
As SARS-CoV-2 transitions to endemicity and respiratory syncytial virus (RSV) and influenza re-establish their seasonal circulation patterns, understanding their comparative burden on infants and children can guide health-system responses and funding priorities.
Methods
Population-based cohort study of children aged <5 years in Ontario, Canada from September 2018 to August 2023 using linked health administrative databases.
Results
Seasonal cohorts comprised 731,838-763,660 children. RSV and influenza-related hospital admission rates immediately decreased in March 2020. In 2021-22, RSV-related admissions rebounded but remained 8-11% lower than pre-pandemic seasons, whereas 2022-23 RSV-related admissions increased 105-113% versus pre-pandemic seasons and peak admissions occurred in November versus December. Influenza did not rebound until 2022-23 when admissions were 28-37% higher than pre-pandemic seasons. COVID-19-related admissions remained low until 2021-22 and were lower than RSV-related admissions across all age groups during pre-pandemic and pandemic seasons. By contrast, 2021-22 COVID-19-related admissions exceeded pre-pandemic influenza-related admissions by 30-40% but decreased by 45% in 2022-23 and were lower than pre-pandemic influenza-related admissions, except among infants aged <12 months who remained at highest risk. There was no distinct seasonal pattern for COVID-19-related admissions during the study.
Conclusions
RSV remains a major cause of childhood hospitalization. Although COVID-19 appears to be receding, its disease burden as it transitions to endemicity remains to be established. The unprecedented peaks in RSV-related hospital admissions during 2022-23, together with the return of influenza and ongoing SARS-CoV-2 transmission, underscore the need to strengthen systems for real-time surveillance and to proactively prepare for critical healthcare scenarios.
