Changes in Hospital Admissions Associated with Pediatric Respiratory Syncytial Virus after the COVID-19 Pandemic in Canada: an Active Surveillance Study.

BACKGROUND:The COVID-19 pandemic affected the epidemiology of respiratory syncytial virus (RSV). We sought to describe tertiary care hospital admissions associated with pediatric RSV in 2022/23 in Canada and to assess pandemic-related changes. METHODS:We conducted active surveillance of hospital-admitted infants and children aged 0 to 16 years at 13 Immunization Monitoring Program, Active (IMPACT) centres. We compared RSV-associated hospital admissions in 2022/23 with those in the prepandemic period (2017/18 through 2019/20). We calculated province-specific and age-stratified proportions of all-cause hospital admissions with RSV detection and age-stratified proportions of RSV-associated intensive care unit (ICU) admissions. We performed seasonal autoregressive integrated moving average (SARIMA) time-series analyses. RESULTS:In 2022/23, 5362 RSV-associated hospital admissions occurred, including 1260 (23.5%) ICU admissions, both more than double the prepandemic yearly averages. Overall, the median age increased from 6 (interquartile range [IQR] 1 to 20) months to 9 (IQR 2 to 27) months (p < 0.001). The proportion of RSV-associated hospital admissions among all-cause admissions increased by 3.5 percentage points (95% confidence interval [CI] 3.3 to 3.7 percentage points), to 6.8% (95% CI 6.6% to 7.0%). Whereas 41.5% of RSV-associated hospital admissions were among infants younger than 6 months, this age group accounted for 62.1% of ICU admissions. Overall, the ICU proportion remained constant; however, the odds of ICU admission among infants younger than 6 months increased (adjusted odds ratio 1.35, 95% CI 1.2 to 1.52) compared with the prepandemic period. National weekly incidence in 2022/23 peaked earlier and higher, and persisted longer than expected by SARIMA. INTERPRETATION:In 2022/23, the number of RSV-associated hospital admissions and ICU admissions increased dramatically in Canadian pediatric hospitals. The greatest burden remained in infants younger than 6 months. Strategies for RSV immunization for young infants may have a substantial public health impact.