The 2025 measles resurgence in Ontario, Canada validates emerging seroprevalence concerns...Ariyarajah A, Crowcroft NS, Brown KA et al. Measles seroprevalence among individuals serologically tested in Ontario, Canada. Vaccine. 2025;62.

The article discusses the resurgence of measles in Ontario, Canada, in 2025, highlighting significant immunity gaps identified in a seroprevalence study involving approximately 350,000 individuals. Public Health Ontario reported over 2,000 confirmed measles cases, the highest since the disease was eliminated in Canada, with adolescents and young adults being the most affected groups. The findings indicate that immunity levels in these age cohorts fall below the herd immunity threshold of 90-95%, raising concerns about transmission risks, particularly among unvaccinated households and vulnerable immigrant populations. The article emphasizes the need for targeted vaccination campaigns and improved immunization tracking to sustain measles elimination efforts in Canada.