What comes next for Canada’s measles surge

Immunologist Dawn Bowdish tells us why measles cases are soaring, who’s at risk and how we can still stamp it out
An image of a smiling woman in front of illustrations of pathogens

If there was an award for most contagious virus, measles would be a frontrunner. It can hang in the air for hours, and one infected person will pass it on to almost everyone around them who’s unvaccinated. One in five people infected require hospitalization, and nearly one in 300 infected children die. Long-term complications include pneumonia, blindness, ear infection–induced deafness and even a potentially fatal neurological disorder called subacute sclerosing panencephalitis. 

Thanks to high childhood vaccination rates—92 per cent nationwide—Canada typically experiences only a handful of measles cases annually. But 2024 is different. There have been almost twice as many cases so far this year as in all of 2023, and officials say community transmission, which can occur when vaccination rates fall below 95 per cent, may be beginning in parts of Ontario and Quebec. 

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McMaster University immunologist Dawn Bowdish believes Canada may be on the cusp of a serious problem, as vaccine refusal and pandemic-related vaccine disruptions—15,000 kids missed shots in Ottawa alone between 2020 and 2022—create a perfect storm. Here, Bowdish explains why Canada has become more vulnerable, and why a measles outbreak could bring a serious reckoning for our overstretched, under-resourced health system. 

Why should we be worried about measles?

Measles was the deadliest vaccine-preventable infection before the advent of antibiotics and vaccines, and it still is in parts of the world without good vaccination programs. It’s a respiratory virus, so it’s inhaled, just like COVID or influenza or RSV. But instead of affecting the cells that line our lungs and noses, it kills our immune cells. Some of those are memory cells, which hold all our immune experience: every vaccine you’ve ever had, every pathogen you’ve ever encountered. Consequently, we lose some of that immune memory. Historically, after a measles infection, people would get sick from the bacteria that normally live harmlessly in them; you could get fatal pneumonia from the microbes in your nose and mouth. 

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And those immune cells that have been killed don’t come back to the same levels, or with the same function they had. Somebody who’s had measles is more likely to have other infections—we don’t really know how measles and strep A will work together, for example—and will be more likely to need other antibiotics or medical care. One of the things I worry about is that pathogens are more resistant to antibiotics than in the past, due to overuse and because we haven’t had many new antibiotics invented. So infections that were once treated may not be treatable anymore. 

Canada technically eliminated measles in 1998, but cases have always popped up from time to time. Why is what we’re seeing now more worrisome? 

Historically, outbreaks in Canada have happened when somebody who wasn’t vaccinated brought it back from a country where it was endemic. Usually what followed was a concerted effort to test and trace to stop transmission. This time, we’re seeing community transmission, meaning that somebody got measles and we can’t trace where they got it from. With our vaccine rates being lower than the 95 per cent, we need to stamp these outbreaks out. If community transmission can be traced and stopped we may not end up having massive outbreaks. But if we don’t? It’s just so incredibly contagious. Remember in 2020, we were testing and tracing COVID cases—but after a certain point we couldn’t find them all. 

Right now, I’m following the U.K. very carefully to decide what our next step should be. The U.K has a terrible vaccination rate, lower than ours. It’s been an epicentre of vaccine misinformation, and it’s an international country, especially in London. If anyone’s going to have a real problem, they will, and we can learn from how they respond. 

What’s going on in the U.K.? 

Their hope was they were seeing an isolated cluster of cases, but now it’s spread to different parts of the country. It looks like they’re seeing increases in community spread. Like us, their testing and tracing system is overextended. They’re at the cusp of having a big problem. I hope they pull it together, but some of their jurisdictions have vaccination rates of less than 60 per cent. How would you get that many people vaccinated quickly? It’s hard to imagine. 

So how bad could things get in Canada?

I hate the thought of this, but we could reasonably expect outbreaks in pediatric cancer centres, for example. We could also see really problematic infections in pregnant people. Measles used to be one of the major causes of birth defects, stillbirths and miscarriages. In the ’90s, there was a concerted anti-measles vaccine misinformation campaign, and many children were not vaccinated at the time. Now, those children have grown up and they may be thinking about starting families. If they get pregnant they’re going to be vulnerable to infections. That could have terrible consequences for both mom and baby. 

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And then we’ve got a huge black box: we don’t know the effects of immunosuppressant drugs. Say someone’s going through chemotherapy. We don’t really know how well their measles immunity will hold up. 

I’d read that pregnant people were more at risk, but I wasn’t aware of the full implications. Should anyone born in those years be checking their vaccination records, especially if they’re hoping to have children soon? 

Absolutely. People who tend not to be vaccinated are people who’ve missed their childhood vaccine, and most of us may not know. We probably never asked our parents, “Did you get my vaccines on time?”

I had to ask my parents yesterday, actually.

Exactly, because how would you know? And Canada, we have all sorts of people here from around the world. If there’s civil unrest, or issues with health-care delivery, many people may be coming to Canada and have missed those childhood vaccines through no fault of their own. 

I can’t imagine you’d think about a measles vaccine when you’re fleeing a war zone. What do you do if you just can’t track down your vaccine record? 

Our National Advisory Council on Immunization has very clear guidelines: if you don’t know, get vaccinated. There are no safety concerns about getting vaccinated again; it just means you’ll be a little more boosted. The measles vaccine is given in a three-in-one for measles, mumps and rubella. It’s free and accessible and part of Canada’s childhood vaccines. What makes it complicated is that each province has different rules for getting a catch-up vaccine. In some places, people have to go to public-health units. In other places, they can get it from family doctors or even pharmacies. 

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But that’s part of our problem too. Most people get their childhood vaccines from a family doctor, and many Canadians don’t have a family doctor right now. We’re unclear how much the family doctor shortage is impeding childhood vaccines, but that’s one of the reasons vaccination rates are falling. This is public health 101. When it works, it’s so seamless that everyone takes it for granted. But right now, we have lots of problems at the same time: the family-doctor crisis, the vaccine-misinformation crisis, funding issues and our over-extended public health officials who are still dealing with COVID and pandemic-related things.

You mentioned vaccine misinformation. It feels like anti-vax sentiment has also really taken off since the pandemic began. 

We were so close at certain points to globally eliminating measles or making it extremely rare. But as misinformation accelerated during the pandemic, we saw the opposite. People are now less likely to get their children vaccinated than before. Everything’s condensed to make this situation so worrisome. We have a stretched public health system that’s not resourced to do the contract tracing that you need for a measles outbreak. We have more vaccine hesitancy. And frankly, people have forgotten how bad measles is. It was news to you about birth defects and stillbirths. It was not news to our great-grandparents and grandparents.

How can Canada’s public-health authorities tackle this problem in the short term?

If I could make a wish list right now, one of the things on it would be catch-up clinics. They could go to schools, where kids already are. And if we want to get serious, we already know which areas have particularly low vaccination rates. Setting up clinics at those spaces would be helpful.

Also, more surveillance. With public health, you have to be proactive, and right now we can’t make the best decisions because we don’t have data available. I don’t know if our patients in cancer centres are going to be vulnerable. I don’t know if we might have terrible outbreaks in long-term care. I don’t know what percentage of people in their reproductive years have immunity. And I don’t know who would best benefit from a booster campaign. 

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Early in the pandemic, I remember a colleague and I were talking about how we should start looking at whether or not measles vaccine immunity was waning, because measles is a constant threat and it suppresses the immune system. But there was no interest in funding that kind of work, because measles wasn’t seen as a problem. 

You know a lot about vaccines. How do you talk to a loved one who’s hesitant to get vaccinated against measles?

Especially for measles, one of the things that I’ve found helpful is to explain why it’s so bad—that it kills your immune cells and leaves you vulnerable to things you would’ve otherwise been protected from. The other thing is that the measles vaccine has been with us for a really long time. Many of the concerns that people had about the COVID vaccines being too new and developed too quickly aren’t there for measles. The vast majority of people born after 1968 have been vaccinated without suffering any effects. 

But the most important thing is to listen to people’s concerns. What you think they’re worried about might not match up with what they’re actually worried about. Different people have different concerns, and some of them may have heard very specific misinformation. 

If we can’t get vaccine rates back up, what’s at stake? 

One of the things that’s unique to our time is the increased rate of antibiotic resistance. Infections that once were trivial will become more and more serious—but vaccinations can prevent those infections in the first place. Second, any serious infection during pregnancy can make pregnancy more complicated. It can lead to premature births and a higher risk of neurodevelopmental disorders in children. Obviously, you want to prevent those things if you can. Finally, infections when you’re older can have really serious health complications and cause age-related conditions to accelerate. And our health-care system is so overburdened as it is. Whenever we have more infections, especially vaccine-preventable infections, we’re reducing the amount of care we can get for everything else.