Vaccine-preventable disease specialists say the severity of the situation in Canada will depend, to a degree, on chance.ANDREW TESTA/The New York Times News Service
A worldwide surge in measles cases combined with lower vaccination rates and one of the year’s busiest travel seasons has many health professionals on high alert for outbreaks and preparing an urgent response to stop further spread of the highly contagious virus.
A measles expert with the World Health Organization said the next few months will be a test of Canada’s vaccination systems and could expose potential weaknesses.
“This is where we find out whether or not the immunization systems are as good as we think,” said Natasha Crowcroft, senior technical adviser for measles and rubella with the WHO. “You can go along thinking everything is fine until measles takes off everywhere.”
There have been nearly two dozen confirmed cases of measles reported in Canada so far this year, compared with just 12 in all of 2023. Of this year’s cases, 12 are in Quebec, with the Montreal area experiencing community transmission of the virus in areas with low vaccination rates. This past week, B.C. confirmed its first case of measles since 2019.
Health officials have urged March break travellers to be cautious, given the increased measles spread worldwide.
The return of measles is cause for concern, not disdain
Vaccine-preventable disease specialists say the severity of the situation in Canada will depend, to a degree, on chance. If an individual acquires measles on an international trip, but lives in a highly vaccinated community, the risks are lower. But if a measles case is introduced into an unvaccinated area or even a hospital with many immune-compromised patients, the situation could be much more difficult to manage.
“It’s always sort of the luck of the draw, where will that imported case come to,” said Monika Naus, medical director of Immunization Programs and Vaccine Preventable Diseases Service at the BC Centre for Disease Control. “That risk is higher if those imported cases come into an under-vaccinated population.”
There was a 79-per-cent increase in measles cases around the world last year, reaching more than 300,000, according to the WHO. Experts say a combination of factors, including disruptions to immunization programs during the pandemic, lack of access in lower- and middle-income countries and vaccine hesitancy or anti-vaccine beliefs, are all part of the problem.
How effective is the measles vaccine?
The measles, mumps and rubella vaccine is around 95 per cent effective, meaning five per cent of those who get it remain susceptible. Imagine a group of 100 individuals, in which 95 are vaccinated and five are not. The unvaccinated people are at risk of catching measles, as are five people in the vaccinated group. If all 100 are exposed to the virus, the five unvaccinated and five of the vaccinated individuals will likely become infected. In the end, 5.3 per cent in the vaccinated group will get sick, compared with all the unvaccinated individuals.
Immune-vaccinated
Susceptible-
vaccinated
Susceptible-
unvaccinated
carly weeks and john sopinski/the globe and mail,
Source: Bc Centre for disease control
How effective is the measles vaccine?
The measles, mumps and rubella vaccine is around 95 per cent effective, meaning five per cent of those who get it remain susceptible. Imagine a group of 100 individuals, in which 95 are vaccinated and five are not. The unvaccinated people are at risk of catching measles, as are five people in the vaccinated group. If all 100 are exposed to the virus, the five unvaccinated and five of the vaccinated individuals will likely become infected. In the end, 5.3 per cent in the vaccinated group will get sick, compared with all the unvaccinated individuals.
Immune-vaccinated
Susceptible-
vaccinated
Susceptible-
unvaccinated
carly weeks and john sopinski/the globe and mail,
Source: Bc Centre for disease control
How effective is the measles vaccine?
The measles, mumps and rubella vaccine is around 95 per cent effective, meaning five per cent of those who get it remain susceptible. Imagine a group of 100 individuals, in which 95 are vaccinated and five are not. The unvaccinated people are at risk of catching measles, as are five people in the vaccinated group. If all 100 are exposed to the virus, the five unvaccinated and five of the vaccinated individuals will likely become infected. In the end, 5.3 per cent in the vaccinated group will get sick, compared with all the unvaccinated individuals.
Immune-vaccinated
Susceptible-
vaccinated
Susceptible-
unvaccinated
carly weeks and john sopinski/the globe and mail, Source: Bc Centre for disease control
Canada eliminated measles in 1998, meaning the virus no longer spreads on its own here; cases are typically introduced through international travel. But if transmission of the virus here continues for more than a year, Canada will lose its measles-free status. That almost happened in 2011, after a major outbreak in Quebec that led to nearly 800 cases.
A 2012 study of that outbreak, published in the Journal of Infectious Diseases, noted that many of the cases spread in school students who had one or two doses of the measles vaccine. But overall vaccination rates were below 95 per cent, which is the threshold needed to keep the virus at bay, according to the WHO.
The study concluded that, considering a small number of vaccinated individuals will remain susceptible to the virus, having even 3-5 per cent of people unvaccinated could be enough to “push the population toward a critical tipping point for epidemic risk.”
Another large outbreak occurred in B.C. in 2014. The outbreak was mainly confined to a religious community that opposes vaccination. But Dr. Naus noted the outbreak didn’t spread beyond the community because of efforts undertaken by its members and public health.
She said that during outbreaks in that community and others that oppose vaccines, health workers will often set up quasi-undercover immunization centres where community members can get vaccinated without anyone else knowing.
“People, members of the community, didn’t want to be shunned by family or friends if they did come forward,” Dr. Naus said, adding that it’s essential for public health to establish trust and maintain communication with communities that reject vaccines.
Health officials say that Canadians who plan on travelling internationally should ensure they’re up to date on their vaccinations. People born before 1970 are presumed to have immunity from the era when measles was highly prevalent in Canada and should receive one dose to ensure they are immune. For people born in 1970 or later who have not previously been vaccinated or infected with measles, two doses are recommended. Officials advise individuals to check with their health care provider, but given that Canada doesn’t have a national vaccine registry, figuring out who has been vaccinated can be a challenge.
Babies are eligible for their first dose of measles vaccine at one year. Babies aged six to 12 months can get a vaccine if they are travelling internationally (but still require another dose at 12 months).
Measles is one of the most contagious viruses in existence. Almost everyone who comes into contact with the virus will get infected if they aren’t vaccinated or immune from a prior illness. The virus can remain suspended in the air for two hours, meaning a person doesn’t even have to be in the room at the same time as an infected individual to catch it.
One in five people infected require hospital admission. One in 10 will develop a complicating infection, such as pneumonia, while one in 1,000 will develop brain inflammation, which can cause severe problems, including deafness and intellectual disability. Up to three in 1,000 people infected with measles will die.
That’s why health officials are quick to raise the alarm after even a single case is reported, a situation playing out in the York Region of the Greater Toronto Area. On Feb. 29, York Region Public Health said it had confirmed measles in an adult male in his 30s who had not recently travelled or been in contact with a measles case. He was fully vaccinated and his illness was mild.
As soon as the case was confirmed, health officials alerted about 1,800 close contacts and identified those at highest risk for severe complications. So far, no reports of transmission have occurred.
An alert was sent out to advise the public of places the man had visited before he went into isolation. York Region’s associate medical officer of health, Sarah Erdman, said the health unit set up a vaccine clinic and a post-exposure prophylaxis clinic to target higher-risk groups. A person who is exposed to measles has a 72-hour window to receive a vaccine or, in the case of infants under six months, pregnant women or those with compromised immune systems, a blood product containing measles antibodies, to help ward off complications.
Back at the World Health Organization, Dr. Crowcroft said that vaccination rates have been falling around the world, creating a “perfect storm” of risk.
“We’re in a really urgent emergency situation for the rest of the world,” she said. “I don’t get the sense this is being taken seriously. We need urgent action now.”
Editor’s note: This article has been updated that two doses of the measles vaccine are recommended for people born in 1970 or later who have not previously been vaccinated or infected with measles.