Research in Action: RSV Immunization Shows Strong Protection for Infants

A new Canadian study led by researchers from Public Health Ontario and partners across Canada through the SPRINT-KIDS Project found that nirsevimab, a long-acting immunization that helps protect infants against respiratory syncytial virus (RSV), reduced RSV-related intensive care unit admissions by 97 per cent and cut RSV-related hospital-based care by nearly 80 per cent during the 2024–25 RSV season, underscoring its effectiveness in preventing severe RSV illness in infants.

The study analyzed data from nearly 2,000 infants under one year of age who were tested for RSV at seven paediatric hospitals in Ontario and Quebec. Infants who received nirsevimab were significantly less likely to need emergency department care, hospitalization or intensive care for RSV infection.
RSV is a leading cause of hospitalization among infants and young children. In fall 2024, Ontario and Quebec became the first Canadian provinces to offer publicly funded universal access to nirsevimab for infants entering their first RSV season.

The results showed strong protection: nirsevimab reduced the risk of RSV-related emergency department visits by 77 per cent, hospitalizations by 79 per cent and intensive care unit admissions by 97 per cent. Overall, infants who received nirsevimab had a 78 per cent lower likelihood of developing RSV illness requiring hospital-based care compared with those who did not receive the immunization.

Protection remained high across infant populations, including babies born prematurely and those with underlying health conditions, and was consistent by age group and province. The findings provide early Canadian evidence that publicly funded RSV immunization programs can help prevent severe illness in infants and reduce pressure on hospitals.

About the study

The study was conducted through the Surveillance Program for the Rapid IdeNtification and TracKing of Infectious Diseases in kidS (SPRINT-KIDS), a national pediatric infectious disease surveillance network. Funding was provided through the Public Health Agency of Canada.