Should you get another measles shot? What to know as cases surge

With measles cases on the rise in Canada, some adults may be questioning whether their immunity, either through natural infection or vaccine, is still strong enough.

With measles cases on the rise in Canada, some adults may be questioning whether their immunity, either through natural infection or vaccine, is still strong enough.

While many Canadians receive two doses of the measles vaccine in childhood, those born after 1970 may have only received one — and their protection could have weakened over time.

Routine measles vaccinations didn’t begin in Canada until 1970, and even then, a second dose wasn’t added to the schedule until 1996, leaving some adults with incomplete protection.

“People born in, for example, 1971 aren’t that young anymore, and they might have received two doses of a measles vaccine or one dose of a vaccine, but they may not have the same degree of immunity,” said Dr. Isaac Bogoch, an infectious diseases specialist at Toronto General Hospital.

“There probably are a lot of people who think they’re vaccinated who have only had one dose, and the recommendation is if you’re traveling to places where there’s a lot of measles circulating and you only had one dose, you should get a second dose,” Bogoch added.

Measles is one of the most contagious infectious diseases — more contagious than diseases like COVID-19, influenza and chickenpox. This high level of contagiousness is one reason why measles outbreaks can spread rapidly, particularly in areas with low vaccination rates.

So far this year, Canada has reported 95 cases of measles (as of Feb. 21), with British Columbia, Manitoba, Ontario and Quebec bearing the brunt of the outbreak, the latest data from the Public Health Agency of Canada (PHAC) shows.

The measles vaccine is available in Canada as measles-mumps-rubella (MMR) or measles-mumps-rubella-varicella (MMRV) vaccine. It’s estimated to be 85 to 95 per cent effective after a single dose given at 12 or 15 months of age. With a second dose, efficacy rises to nearly 100 per cent, according to PHAC.