Canada officially eliminated measles in 1998, but recent outbreaks of the highly contagious virus have public health officials urging people to get vaccinated.
Dr. Gerald Evans is the Medical Director of Infection Prevention and Control at Kingston Health Sciences Centre (KHSC), and a professor at Queen’s University with decades of experience in infectious disease management and prevention. With dozens of confirmed measles cases in the South East Health Unit, Kingstonist spoke to Evans on Thursday, Apr. 3, 2025, to find out why this resurgence is happening and how we can best protect ourselves and our communities.
Evans confirmed that as of Thursday, there were 36 cases of measles in the South East Health Unit, the new public health agency formed on January 1, 2025, through the merger of three legacy public health units: Kingston, Frontenac, Lennox & Addington Public Health; Hastings Prince Edward Public Health; and Leeds, Grenville, and Lanark District Health Unit).
“We have a total of 665 cases in Ontario, of which 540 or so are confirmed cases, and 125 are waiting confirmation,” Evans said. “Confirmation usually means we do a blood test on you to prove it’s measles. But probable cases of measles always turn out to be confirmed cases; once you’ve seen a few cases of it, it’s an easy diagnosis to make. And almost everybody who’s been affected has been unvaccinated.”
He called measles “the quintessential airborne virus,” explaining, “This virus is spread through very tiny aerosol droplets, as well as contact and other things, and this virus is stable in the environment. So if you go into a room where a patient who had measles has been, even a few hours later you can actually get measles if you’re susceptible to catching it. So [it is] very, very transmissible, and [in] the typical kind of way that many viruses are transmitted.”
Resurgence traced to Mennonite gathering
In a Friday, Mar. 7, 2025, letter to Ontario’s health units, the province’s Chief Medical Officer of Health, Dr. Kieran Moore, said there was “an exposure at a large gathering with guests from Mennonite communities in New Brunswick last fall.”
Evans explained that vaccination rates in the Mennonite community have been historically low, and “there was a case of measles that spread across most of the provinces. All [provinces] have reported a case except the Maritimes, which is surprising.”
The gathering was large and involved people from all over Canada who then travelled back to their home provinces, bringing measles with them. “And because it’s a vast group of people across the country in various unvaccinated communities, those were all the cases,” Evans said.
“There have been cases outside that group,” the infectious disease expert acknowledged. “We always get cases imported into Canada from other countries where measles vaccination is not as high. And right now there’s an explosion of measles in Europe in general. There’s also, as you know, an ongoing outbreak in the United States, centred in Texas — again, same religious community (Mennonite) — and has since spread to… 10 or 11 states from there. So there’s a small number of [cases] that have been imported. Still, the vast majority in Canada are related epidemiologically to that [New Brunswick] exposure and subsequent transmission in these communities to others. In Ontario, most cases have been in the southwestern part of the province.”
According to the University of Waterloo’s Conrad Grebel University College website, there are about 175,000 Mennonites in Canada, and about 59,000 in Ontario. Mennonite groups are found across Canada, with over half the population residing in urban areas such as Winnipeg, Vancouver, and Kitchener-Waterloo.
Evans noted another critical point about the spread of the disease: “Here in Ontario, what’s been happening with this outbreak is that every week we’re seeing some routine 50 and 100 new cases. So that’s pretty substantial. Now, they are again occurring primarily in unvaccinated communities, so the risk to the general public is relatively low.”
He emphasized, “Here in southeastern Ontario, the vaccination rate amongst the general population is 96 per cent, so that’s great; that’s about as good as you can get. It certainly gives us herd immunity, meaning that if somebody around here is exposed, the likelihood that the virus is going to be able to transmit within our community of vaccinated people is very low.”
If a person can’t get vaccinated due to underlying health reasons, Evans said, herd immunity will be an effective protection for them.
40- to 55-year-olds should consider booster
Most adults have no need to worry, “If you were born before 1970, you do not need to get another measles vaccine. Why? Because you probably had measles when you were a kid. Measles was still widespread right up until the 1970s. I was born before 1970, so I had measles.”
However, he continued, “If you were born between 1970 and 1985″ — here he took a dramatic pause, knowing this reporter is 49 — “you probably only got one dose of the measles vaccine. I’m saying to people your age, maybe you should get a second shot. Because if you were born after 1985, then you probably had two shots: you had one when you were a year old and another before you went into school. Or in the early 90s, we were vaccinating teenagers and stuff like that to give them a second dose.”
“So, you’re in the little cohort, the 15 years between 1970 and 1985, where I would probably hazard a guess that you only got the one shot, because that was the standard to do. And we learned in the late 80s, early 90s, that some people don’t have a long enough immune response, and that’s why we now standardly give two shots: one when you’re a year old and another just before school.”
Evans quickly added, “I would like to reassure people we have very high vaccination rates here in the southeast, particularly in KFL&A. So in general, I don’t think people should necessarily be worried about it.” However, he still recommends that later Generation X and early Millennials get a booster.
He also reiterated that “at the moment, [measles] appears to be confined to communities where they don’t get vaccinated, and so they’re highly susceptible.”
The most contagious viral disease
Evans then emphasized how contagious measles is: “At the moment, this is the most contagious viral disease we know about. I couldn’t say that in the 1800s because then I’d have to say smallpox, but [that’s] not on the planet anymore.”
Measles spreads quickly through respiratory droplets when an infected person coughs, sneezes, or breathes, so “the chances are that if one person is infected and exposed to 20 people who are also susceptible, 18 of those people will become infected.”
He compared that to a disease we are all too familiar with, COVID-19: “If you’re infected with COVID and you get a bunch of susceptible people, only about three or four will get infected. So that’s how much more contagious measles is.”
Measles is not a benign disease either, he said: “Of all the things you can get when you’re a kid — chicken pox, measles, German measles, mumps, you name it — this is the most deadly. One in 1,000 people will die from measles.”
“Measles is serious because it has a lot of complications associated with it. The two most common ones we see are pneumonia and encephalitis (brain inflammation). Encephalitis, in particular, can be quite deadly. It will leave what we call sequelae or followup problems with brain damage, which can result in significant long-term effects over the life of the person, if they survive,” said Evans.
“Pneumonia is particularly dangerous as well, and patients sometimes need to be cared for in a hospital and may need to be ventilated.”
He spoke of how this was the case before a vaccination was developed.
“It’s important to remember that back in the days when measles was around, we didn’t have the vaccine. Everybody got measles. Almost everybody recovered from it, but a substantial number of people would get sick enough that they might have to go to the hospital. I never did when I had measles with my sister; we just were at home, and we were sick for a week or two, and then we got better,” Evans said.
“But some people do have to go to hospital. And like I said, one in 1,000 are actually going to die from a complication, either measles pneumonia or measles encephalitis.”
The doctor said that people compare measles to chicken pox, mumps, or German measles, but, he stressed, “the mortality rate with this is much higher than those, so it’s the most serious of all the childhood viral infections that we currently vaccinate people against. I think it’s just important for people to know that.”
“This is the classic thing, when your mom said, ‘An ounce of prevention is worth a pound of cure,’” Evans said. “That’s measles we’re talking about.”
Vaccination, vaccination, vaccination
Evans said frankly that the only real prevention is vaccination.
“Measles is so contagious that even those measures [we took during the pandemic, such as masking, etc.] in no way match up to what vaccination is,” he expressed.
“So the answer, when it comes to the prevention of measles, is vaccination, vaccination, vaccination. Those other measures are not going to be particularly useful.”
If you suspect you have measles or have been exposed to a case of measles, Evans said, you should call a doctor for advice and notification: either your personal physician, a clinic, or an emergency department.
“Public Health has to be notified. This is considered a notifiable disease, and even if it’s just a concern about exposure, Public Health will follow up and do contact tracing of the suspected case and others who may have been in contact with them,” he said.
To learn more about measles, watch this video created by KHSC, ‘Asking an expert about measles — featuring Dr. Gerald Evans.’
