Waning measles immunization rates means risk of virus's return to Canada: experts

With infections and deaths linked to measles soaring abroad, medical experts warn that waning immunization rates are increasing risks of the virus’s return to Canada.

Recently released international data from the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) show that in 2022, rates of measles infection rose by 18 per cent globally over the year prior, with deaths attributed to the disease rising 43 per cent in that time and 37 different countries reporting large or disruptive outbreaks.

Last updated in August of last year, the Canadian government currently maintains a global health notice for measles, warning would-be travellers of the mounting risk of outbreaks around the world and encouraging they make sure they are protected from infection well before they leave Canada.

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Domestically, the measles virus has been both infrequently encountered and tightly monitored for years, with just 12 cases nationally in all of 2023, according to the Public Health Agency of Canada (PHAC). But amid fears of Canada’s immunization rates dipping during the COVID-19 pandemic, risks have grown that measles, another potentially life-threatening virus, could make a return.

“So far, we’ve been lucky in Canada,” said Joan Robinson, a physician and specialist in pediatric infectious disease at Stollery Children's Hospital in Edmonton, in an interview with CTVNews.ca.

“I think there’s lots of reason to think the chance is really high that over the next five years, we’ll start to see more and bigger outbreaks.”

Highly contagious, but vaccine-preventable: WHO and CDC

Measles typically cause a rash, fever, cough and runny nose, and, in North America, is most commonly found among younger people. In rare, serious cases, complications of infection can trigger respiratory failure and inflammation in the brain, which can in turn lead to hearing and vision loss, as well as neurological damage. Among pregnant patients, measles can also increase risks of miscarriage, premature labour and low birth weight, according to the PHAC.

Some of the most serious impacts of a measles infection can take years to develop, including subacute sclerosing panencephalitis, a rare and fatal disease of the nervous system that can manifest as late as a decade after the initial infection.

Among the virus’s most notable attributes is its contagiousness. The CDC estimates that without protection, roughly nine in 10 of those exposed to the measles virus will develop an infection, and in order to achieve immunity on the population level, WHO guidelines note that 95 per cent or more of individuals must be fully vaccinated.

As Robinson describes, without that kind of immunity, it’s easy for an outbreak to get out of hand.

“If measles were introduced in a classroom … over the matter of weeks, there could be exponential spread,” she said. “Another problem is that children who are not immunized tend to cluster together … you certainly have pockets where there’s very low immunization rates.”

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Today, measles vaccines are typically administered in two doses starting one year after birth, and as a result of monumental international effort, childhood vaccination against the disease is widespread in many countries, with the WHO and CDC estimating that as many as 57 million deaths have be averted via measles vaccination since 2000.

Statistics Canada data published last year found that in 2021, roughly 92 per cent of Canadian two-year-olds had received their measles vaccination, and a separate 2022 study by a consortium of national public health experts found signs of immunity in 90 per cent of samples collected for the Canadian Health Measures Survey.

“The data is absolutely convincing that the measles vaccine is incredibly effective,” said Robinson. “As far as we know, if you’ve had those two doses, you’re incredibly unlikely to ever get measles.”

Since the introduction of measles vaccines in 1963, annual rates of reported infection have dropped profoundly in Canada, from more than 60,000 reported cases in 1951, to 25,000 by 1970 and just over 200 by the year 2000. In the nearly four years since the outset of the COVID-19 pandemic, Health Canada counted just 16 confirmed cases of measles, nationwide.

Abroad, though, is a different story.

Estimates released by the WHO and CDC in November showed more than nine million cases of measles globally in 2022, up from 7.8 million the year prior. Between June and November of last year, countries with the most cases included Yemen, with roughly 23,000 total cases, India, with 14,000 and Kazakhstan, with 12,800.

The WHO/CDC report pointed to COVID-19’s interruption of regular vaccination protocols as a key problem, with 33 million children missing their first or second dose in 2022 alone.

“It is critical that all countries and global partners work to accelerate the recovery of vaccination and surveillance programs,” the report concludes.

The long road to immunity

In 2019, global vaccination rates for measles reached an estimated 86 per cent for at least a single dose, jumping from 72 per cent at the turn of the millennium, according to the report. Since then, the trend has fluctuated, with global rates dropping to between 81 and 83 per cent throughout the pandemic.

Among low-income countries, where the WHO and CDC note the risk of death is likely highest, vaccination of at least one dose sat at just 66 per cent in 2022.

“The lack of recovery in measles vaccine coverage in low-income countries following the pandemic is an alarm bell for action,” said WHO immunization director Kate O’Brien, in a November press release. “Children everywhere have the right to be protected by the lifesaving measles vaccine, no matter where they live.”

One study from the University of Toronto found that early in the pandemic, coverage of the measles-mumps-rubella vaccine fell by 1.7 per cent among a sample of Ontarian children under the age of two, nearing the two to five-per-cent range of vaccination decrease the study authors wrote is associated with exponential growth in the size of measles outbreaks.

“Interventions for providers and parents are needed to ensure adequate catch-up of delayed/missed immunizations to prevent potential outbreaks” the study concluded.

Robinson notes that it isn’t just a healthcare capacity issue. With years of pandemic politics still fresh in the minds of many, there are also political forces to reckon with.

“As the pandemic progressed, COVID vaccine became incredibly controversial,” she said. “I think that because of that, many parents decided that maybe all immunizations were somewhat controversial.”

It’s not the first time vaccine hesitancy has arisen, but to Robinson, what makes this time different is its capacity for those communities to grow and communicate.

“We all know on social media, you tend to follow the people whose opinions you agree with,” she said. “You can readily find large numbers of people who make you feel like you’ve made totally the right decision for your child, and I think that’s a huge difference.”

But as efforts to increase vaccine coverage grow complicated, Robinson points out an advantage that the fight against measles has on some others: the lack of any known transmission between humans and animals.

“In the same way that we’re trying to eradicate polio, we could actually eradicate measles,” she said.

“If you could immunize everyone, that would be the end of it.”

Edited by CTVNews.ca Special Projects Producer Phil Hahn