Health officials in New Brunswick declared a measles outbreak on November 1, 2024, following a large gathering within the Mennonite community. This event was the trigger for an active, continuous measles outbreak in Ontario. It shines a spotlight on just how important vaccination efforts are across the country. The outbreak in Ontario officially ended on January 7. It went on to leave a cumulative 50 cases, most notably focused in the Grand Erie and Southwestern Public Health Unit. While alarming, this surge highlights the threat facing unvaccinated communities. In reality, more than 90 percent of Ontario’s measles cases this year have been in people who are unvaccinated.
The measles vaccine is offered in Canada as the measles-mumps-rubella (MMR) vaccine, or the measles-mumps-rubella-varicella (MMRV) vaccine. A single dose given at 12 or 15 months of age is almost 100 percent effective. It is projected to be about 85 to 95 percent protective. According to Public Health Agency of Canada (PHAC) data, with a second dose, efficacy increases to almost 100 percent. All of this efficacy aside, unvaccinated people are still at great risk, as seen by the recent outbreaks.
By March 18, a cumulative total of 369 cases had been reported from coast to coast in Canada since the start of the year. As of February 26, Ontario was responsible for 177 of those cases associated with this outbreak. Health workers in New Brunswick responded with impressive speed. Their extensive contact tracing allowed them to trace 266 persons and vaccinated 239 of them through a network of 30 clinics. In retrospect, these proactive measures were crucial in preventing spread of the virus.
Dr. Kieran Moore noted that measles cases have been on the rise in southwestern Ontario, and additional exposures from travel over March break are expected to further exacerbate the problem. This risk of higher transmission is a reminder of why we need to continue monitoring and push forward with vaccination.
