What to know about the measles vaccine — from who should get one, to how long immunity lasts

This story is part of CBC Health’s Second Opinion, a weekly analysis of health and medical science news emailed to subscribers on Saturday mornings. If you haven’t subscribed yet, you can do that by clicking here.

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In Canada, measles was once a disease of the past. But it’s increasingly becoming a health threat of the present, after backsliding vaccination rates allowed the virus to creep back into circulation.

Canada officially eliminated measles nearly three decades ago, but for years, medical experts warned it was poised to make a comeback — and disruptions to routine childhood immunization efforts throughout the COVID-19 pandemic may have sped that up.

Now, after tens of thousands of cases in Europe, and close to 100 recent infections across Canada and the U.S., health officials are on high alert.

There are warnings about travel abroad, calls for people to ensure their families are up-to-date on the measles vaccine, and fresh reminders that the virus is highly contagious and capable of causing pneumonia, brain inflammation, and even death.

“A lot of people are worried,” said Dr. Alykhan Abdulla, a family physician in Ottawa. “Measles hasn’t really been around in our society for a long time.”

So how should Canadians navigate the latest guidance around measles vaccination, and who’s actually protected? And if you’ve already had at least one measles shot, are you now set for life?

Who should get the measles vaccine?

If you or your child has never had a combined measles, mumps and rubella (MMR) vaccine — and never had a prior measles infection — the official guidance is simple: Get vaccinated.

But after that, it gets a little more complicated.

For Canadian children, the typical schedule is now two doses, both administered before they enter school. The first MMR dose should be given when a child is 12 to 15 months of age and the second dose at 18 months, or any time after that, but no later than around school entry, notes the Canadian immunization guide. 

As for adults, if you were born after the two-dose MMR vaccine became routine, you probably had both rounds as a child. 

Some adults might’ve only had one dose, however. That includes people born before 1970, who were likely exposed to the virus, given how widely measles used to circulate — and federal guidance assumes those individuals have natural immunity.

However, the same guidance suggests anyone who’s at a higher risk of being exposed — like health-care workers, military personnel and international travellers — should get an MMR vaccine, regardless of their year of birth. 

Confused yet? 

What if you don’t have your immunization record, or can’t remember if you had a measles infection in childhood? Experts suggest simply getting an MMR dose, to be safe.

“If there’s any concern about whether you’ve been vaccinated, it’s actually cheaper and easier just to get vaccinated again,” said McMaster University associate professor and immunologist Dawn Bowdish.

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What do I need to know if I’m travelling outside of Canada?

More than 50 countries are reporting “large and disruptive” measles outbreaks, World Health Organization officials warned this week.

So if you or a family member hasn’t been vaccinated against measles before travelling, there’s a higher risk of catching it, medical experts warn, making it even more important to be up-to-date on your shots.

That’s because measles is capable of lingering in the air for up to two hours (yes, hours) after someone infected enters a space.

Infants under the age of one are “particularly vulnerable” to a measles infection, according to the Public Health Agency of Canada (PHAC), since their routine shots typically start at 12 months of age.

In a statement, PHAC told CBC News the current advice for people travelling internationally is as follows:

• Infants between six months and less than 12 months of age: One dose if they’re travelling to a high-risk area. (However, that shot will be considered “dose zero” on their record, as children who get an early dose will still require two more doses later.)
• Children and adolescents: Two doses.
• Adults born in 1970 or later: Two doses.
• Adults born before 1970: At least one dose.

If people need a shot, how can they get one?

If you need an MMR shot, medical experts suggest speaking to your primary care provider such as a family doctor or nurse practitioner — if you have one — or reaching out to your local community health centre or public health team.

Travel clinics are also an option to quickly get a shot before a trip, though private businesses can charge $75 or more for a dose.

Still, it’s not always easy.

Despite the guidance around staying up-to-date on measles vaccinations, multiple Canadians told CBC News that some doctors and pharmacies are either short on supply, or simply discouraging patients from getting another round because they’re either deemed too young or too old to need one. 

“I think we’re all adjusting to this reality of measles resurgence from abroad,” said Shelly Bolotin, director of the Centre for Vaccine Preventable Diseases at the University of Toronto. “And perhaps that is why different people are in different places.”

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Is there enough supply of the MMR vaccine available in Canada?

If you do need a dose, there are two MMR vaccines being used in Canada right now, from drug makers Merck and GSK. 

Shortage notices have also been posted for both brands’ shots, but Health Canada said the companies have assured they’ll be able to “fully meet demand” for public immunization programs, including routine childhood vaccines. 

GSK told CBC News the “temporary” shortage for its Priorix vaccine is linked to an increase in demand in the Canadian private market, adding it continues to meet the demand in the public sector. Merck Canada said it is working with provincial and federal health authorities to provide a consistent supply “in a timely manner.”

What’s unclear to Canadian health-care teams is whether an ongoing spike in demand will further complicate vaccination efforts.

“We have to be judicious, we have a resource that is limited,” said Abdulla, in Ottawa. “And we have to be thoughtful in the way that we use [the available supply].” 

Family physician Dr. Allan Grill, in Markham, Ont., said his team is currently distributing measles vaccines on an as-needed basis.

“You can imagine how overwhelmed family medicine would get if we decided all of a sudden to just focus all of our attention on everybody’s measles vaccine status.”

Meanwhile, Andrew Sisnett, president of Summit Health, a travel vaccine provider, said the company rarely doled out MMR shots before this year. Yet demand recently shot up, and he’s having issues ordering more. 

“There are concerns that, from a private-sector perspective, that we’re not going to be able to procure enough.”

How protective is prior infection or vaccination against measles?

If you’ve had a prior measles infection, there’s a silver lining.

Peer-reviewed research from a team including Bolotin stressed that immunity from measles is thought to be life-long.

The study cited evidence from Denmark’s remote Faroe Islands, located in the North Atlantic, which experienced a measles outbreak in 1781. The next outbreak in 1846 spared all those older than 65 — as in, all the people who would have been infected exactly 65 years earlier.

“This early observation remains some of the best evidence of life-long immunity to measles,” the team wrote.

That’s because of how the measles virus operates, Bowdish said.

“Unlike RSV, or influenza or other respiratory infections … it actually infects our immune cells,” she said. “And then it hijacks those immune cells to travel to our lymph nodes, where there’s millions and millions more immune cells to infect.” 

A serious infection like that requires a serious immune response, Bowdish said. It’s a bit like your body fighting a major war, giving it deep, lasting memories of how to fend off that attacker if it ever invades again.

So, is the same thing true for getting a full set of MMR shots?

To some extent, yes.

The measles vaccine contains small amounts of live virus, making it one of the most protective shots available, Bolotin said, with two doses showing 97 per cent efficacy (how well it does in an ideal and controlled environment) in studies, and 94 per cent effectiveness (real-world performance) in field estimates. 

“It’s actually a mini infection in your body. And so it creates something very, very similar to what you would see if you’re infected.”

There can be instances where immunity after the shots does wane over time, both Bowdish and Bolotin agreed, and various global studies have documented occasional breakthrough infections. Even so, evidence suggests the shots still protect against serious illness and help curb transmission. 

“For most vaccines, what we do is we modify or minimize the severity of infections as opposed to preventing them 100 per cent,” said Bowdish.

“But the measles vaccine is a different case, where it really does seem to prevent infections from getting started in most people, most of the time.”