Do I need a third dose of the measles vaccine? And other common questions answered

Jennifer Yoon · CBC News

· Posted: Apr 24, 2025 7:16 PM EDT | Last Updated: 3 minutes ago

It's lone April, and 2025 is already shaping up to beryllium the worst twelvemonth for measles since the illness was declared eliminated successful 1998 successful Canada.

Ontario continues to beryllium the epicentre of the spread. Public Health Ontario is reporting 1,018 confirmed and probable cases of measles truthful acold this year. The immense bulk of those infected were not afloat immunized. Six unvaccinated children and adolescents person been hospitalized with the virus.

In Alberta, too, the microorganism is spreading. The state is reporting 129 cases arsenic of April 24, successful each portion successful the province. In that province, astir of those sick are not afloat vaccinated. Nine radical person been hospitalized. 

Measles is 1 of the astir contagious diseases known to man. Symptoms tin see a fever, coughing and a runny nose, arsenic good arsenic a blotchy reddish rash. In superior cases, measles tin origin complications similar inflammation of the brain, pneumonia and death. 

As the microorganism spreads, present are immoderate communal questions astir immunity to measles, answered. 

Can measles immunity wane?

Two doses of the measles, mumps and rubella (MMR) oregon measles, mumps, rubella and varicella vaccine (MMRV) offer almost 100 per cent effectiveness successful the agelong term.  

Even so, immunologist Dawn Bowdish says she's been fielding questions astir waning immunity from those disquieted they are not perfectly protected from the virus.

"Most of america who were calved aft 1970 person ne'er encountered measles; we've lone been vaccinated. We cognize that a tiny percent of radical successful that script volition person immoderate alteration successful immunity," she said. 

That could mean immoderate breakthrough infections tin hap among those who received 2 doses of a measles vaccine. 

It's a numbers game: the much measles is spreading, the much apt it is that a breakthrough corruption happens, says Dr. Lynora Saxinger, an infectious illness specializer astatine the University of Alberta.

"People who person had 2 doses are substantially protected, but not bulletproof."

Even erstwhile those who are afloat vaccinated get an infection, they're little apt to endure the astir superior consequences, says Dr. Dale Kalina, main aesculapian serviceman astatine Brant Community Healthcare System successful Brantford, Ont., an country that has had measles cases since January.

"The world is [those who've received 2 shots] aren't the radical I would beryllium disquieted astir successful an outbreak, from a dispersed perspective, nor from a complications position oregon a request for hospitalization," helium said. 

How tin I cheque whether I americium protected against measles?

There is simply a humor trial that looks for antibodies against the measles. Whether to get it oregon not is simply a speech radical request to person with their household doctors, says Bowdish.

Health-care workers oregon those who enactment with susceptible radical often get tested for antibodies, arsenic bash immoderate large women. Bowdish says she'd similar to spot that beryllium the modular of attraction crossed the country, due to the fact that measles utilized to beryllium a large origin of mislaid pregnancies, stillbirths and commencement defects successful areas of the satellite with patchy vaccination rates. 

"As we determination to an epoch wherever we person a batch much measles around, I personally americium precise supportive of large women, oregon radical who are readying connected starting a family, getting this test."

WATCH | Getting your kid vaccinated: 

Those who are not definite if they've been afloat vaccinated, though, are amended disconnected getting different dose, alternatively of getting the humor test, says Bowdish. 

"If you can't find your vaccination status, if you came from parts of the satellite that don't person the puerility measles [vaccinations], if you're disquieted that your parents mightiness not person vaccinated you arsenic a kid — our proposal is conscionable get vaccinated," she said. 

Those who are calved earlier 1970 are mostly believed to beryllium protected, says Bowdish, due to the fact that they were exposed to measles arsenic children. 

Do I request a 3rd dose of the measles vaccine?

Canadian nationalist wellness authorities don't urge a 3rd dose of the MMR vaccine for the wide public, even though it's mostly safe. That's due to the fact that it wouldn't marque consciousness to prioritize the constricted clip and nationalist wellness resources we person to springiness a 3rd dose close now, Bowdish says. 

There are immoderate exceptions, similar those who are connected immunosuppressive drugs, oregon crab treatments, Bowdish says. But those decisions should beryllium made aft a speech betwixt the diligent and their doctor. 

Saxinger agrees.

"Making definite that ... people who are unvaccinated get vaccinated archetypal is benignant of the wide priority. There mightiness beryllium a clip erstwhile we would commencement looking astatine the inferior of further doses for much people, but I don't cognize if it's rather now."