The number of confirmed cases of measles in Canada this year has surpassed 2,000 and infectious disease specialists say while the surge will eventually end, continued spread is expected into the summer.
Recent numbers from the provinces show big jumps, with Ontario and Alberta seeing the highest case counts so far.
Ontario reported a total of 173 new cases this past week, bringing the province’s total count to 1,795.
On Wednesday, Alberta reported 19 more cases of the disease, bringing its total to more than 500 — the province’s cases have more than doubled since the beginning of the month.
Manitoba and Saskatchewan have also seen jumps, with the former now at 60 and the latter at 45.
No deaths have been reported in Canada this year, though several hospitalizations have.
“If there’s any case of measles in Canada, that’s too many cases,” said Dr. Isaac Bogoch, an infectious diseases specialist based at Toronto General Hospital.
“But when we’re at, for example, roughly 1,800 cases to date in the country in the 2025 calendar year, that’s way too many cases. We have to actually take a step back and look at what’s driving this.”
According to data from the federal government, an estimated 87.4 per cent of the population has been vaccinated, but due to its high infectivity, at least 95 per cent of the population needs to be immunized for herd immunity.
As the disease continues to spread, especially among under-vaccinated people, cases could continue to be reported well into the summer.
“As long as it’s spreading within networks of under-vaccinated people and there are more of those networks and more people who are under-vaccinated now than in many years past, it will continue to smoulder along,” said Dr. Lynora Saxinger, an infectious diseases specialist at the University of Alberta.
Saxinger said the vast majority of people are protected due to having two doses of the vaccine or, among those born in the 1950s and ’60s, for example, having been infected by measles already.
However, others like the immunocompromised, children and infants who have not been vaccinated yet, and pregnant women are at risk.
“As long as there’s measles circulating, there is enhanced risk for those groups of people and that’s going to be an ongoing concern, I think possibly for some time,” she said.
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Bogoch said he estimates it could “grumble into the summer” and potentially further “until it meets a wall of immunity.”
“It’s going to take a while and a lot of it is dependent on the pace of infection and the exposures throughout the country and the rates of vaccinations for under-vaccinated communities,” Bogoch said.
“There are modifiable factors here. So it’s hard to know exactly how this is going to play out, but I think it’s fair to say that it’s not going to go away tomorrow. It’s going to take months and months for this to dissipate.”
Earlier this year, the outbreak in Ontario was linked back to a “large gathering” last fall in New Brunswick’s Mennonite community, according to the provincial chief medical officer of health, Dr. Kieran Moore.
Other provinces also reported measles cases related to this outbreak.
At the time, Moore said more than 90 per cent of measles cases were among the unvaccinated. As of Thursday, all but 76 cases in that province were linked to this initial outbreak.
Since this spread first began in Ontario, about 76 per cent of cases were in infants, children and adolescents, while nearly 24 per cent were in adults. Of the cases in infants and youth, 96 per cent were among those not immunized while 66 per cent of adult cases weren’t immunized.
The numbers are similar in places like Alberta, with more than three-quarters among children.
Canada is not the only country seeing a surge of cases, with measles also spreading in the U.S. in at least 31 states.
On Friday, the Centers for Disease Control and Prevention (CDC) reported a total of 1,046 confirmed cases across those states, an increase of 22 from last week. At least three deaths have also been reported, two of which were children.
The majority of cases are being reported in Texas, with 728 confirmed since January.
Dr. Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, said in an interview he’s concerned there may be underreporting due to various factors.
“If you look at the doubling rate, you look at the hospitalization rate, and look at the death rate, we’ve had three deaths for a disease that typically kills one in a thousand people,” he said.
“So I think those numbers are just wrong.”
The Children’s Hospital of Philadelphia says approximately one to three in 1,000 children who get measles die from their infection, though UChicago Medicine notes this rate applies to adults as well.
The CDC notes the number of cases reported on its site is based only on confirmed cases, and is aware of probable measles cases being reported by jurisdictions.
“This is the most contagious infection of humans,” Offit said.
“It’s an airspace disease. I don’t have to have direct face-to-face contact with someone who’s sick, I just have to be in their airspace within two hours of them being there.”
Dr. David Sugerman, a senior scientist for the CDC, said last month at the agency’s advisory committee on immunization practice that a large number of cases are being missed by health authorities.
“We do believe that there’s quite a large amount of cases that are not reported and underreported in working very closely with our colleagues in Texas,” Sugermen said in April.
All three health care and infectious disease specialists pointed to vaccines as the key element that could help end this surge.
Offit says it’s also key to get information to communities hesitant about vaccination.
“I think the trick is to find people in that community who are trusted and get them the information they need to try and influence people to do what’s best for their and their children’s health,” he said.
The measles-mumps-rubella vaccine is routinely given in childhood, with two doses recommended prior to school entry, while some may already have immunity from previously being infected.
Though the vaccine is widely available, Saxinger cautions that education is still needed as measles is sometimes thought of as a kid’s rash illness and “benign.”
That’s not the case, she said.
“If you have had two doses of measles vaccine or have had infection in the past, you are considerably protected and so it’s not like a risk to you,” she said.
“But there’s ongoing risks to the community when there’s a spread because some people are not able to have that protection.”
