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“Over the last several weeks, we have seen the number of new measles cases rise to 173, bringing the total number of confirmed cases in Ontario to 350 since 2024, including 31 hospitalizations,” Dr. Kieran Moore said in a press release. “This is the most measles cases Ontario has seen in over a decade.”

Back in January, cases were confirmed in Woodstock, St. Thomas, and Oxford and Elgin counties.

That was followed by cases in Peel Region, York Region, Windsor, London, Hamilton and Haldimand-Norfolk — which also declared potential measles exposures.

Most of the cases are related to international travel.

“Over 96 per cent of cases in Ontario are among individuals who are unimmunized, or have unknown immunization status, and were exposed in their community or while travelling,” Moore said. “A majority of Ontario’s cases are concentrated in southwestern Ontario among unvaccinated people.”

An updated list of potential exposure locations has been shared on ‘s website.

Measles spread

Measles is a highly contagious respiratory virus, with symptoms that can show up within 21 days of exposure. Signs of measles include fever, a red blotchy rash, red, watery eyes and a cough.

There is no treatment for measles — usually it’s rest, drinking fluids and pain relief for headaches. Some severe cases require hospitalization, and it may even lead to pneumonia, encephalitis, and death.

Up until now, the vaccine has been the only real source of prevention.

However, in February, the , saying post-exposure prophylaxis following exposure to measles should be offered to individuals not expected to have measles immunity.

Vaccination most effective prevention

According to health officials, the best prevention to protect against measles is vaccination.

In Canada, measles has been a reportable disease since 1924.

“Before vaccinations, about 10,000 to 90,000 people living in Canada were infected with measles every year,” Health Canada .

A vaccine was first introduced in 1963, and children born after 1970 were commonly vaccinated against measles with a one-dose combination of measles, mumps and rubella vaccine (MMR).

Within a decade, a booster shot was commonly part of the routine, given several years later to boost immunity.

“As part of routine vaccination schedules, children should receive two doses of measles vaccine, with their first at 12 months and a second when they are between four to six years old, preferably before they start school,” the Ontario Ministry of Health said.

This free, two-dose vaccination schedule was so successful in preventing measles transmission, in 1998 “Canada achieved elimination status for measles with endemic transmission no longer taking place.”

However, it was around the same time concerns were raised about the vaccine’s potential connection to autism.

The autism-vaccine connection

A few outspoken experts created public alarm over vaccinations in 1998, believing there may be a connection between the MMR vaccine and autism.

In fact, the theory was reported in the medical journal “The Lancet” by Dr. Andrew Wakefield and colleagues.

In the original paper, a dozen children were referred to the Royal Free Hospital and School of Medicine with chronic enterocolitis and regressive developmental disorder.

“The authors reported that the parents of eight of the 12 children associated their loss of acquired skills, including language, with the MMR vaccination,” the paper noted at the time. “The authors concluded that ‘possible environmental triggers’ (i.e. the vaccine) were associated with the onset of both the gastrointestinal disease and developmental regression.”

Parents began to question vaccination safety, and it gained global headlines after actor Jenny McCarthy adamantly said the MMR vaccine caused her son Evan’s autism in 2007.

However, in 2010, “The Lancet” ended up linking autism to MMR vaccinations.

“The British medical journal said that it is now clear that ‘several elements’ of a 1998 paper it published by Dr. Andrew Wakefield and his colleagues (Lancet 1998; 351[9103]: 637–41) ‘are incorrect, contrary to the findings of an earlier investigation.’”

It turned out Wakefield’s subjects were carefully selected, and his research was partially funded by lawyers acting for parents suing vaccine manufacturers.

Canadian officials were glad to see the retraction.

“I think a lot of families were looking for a reason, so they were extremely vulnerable (to this explanation),” Queen’s University geneticist Jeanette Holden said in a piece at the time. “The problem is that this had dramatic health consequences, which was that people just didn’t vaccinate their children.”

Rethinking vaccination

With measles making the rounds again in some Ontario communities, parents, their older children or unvaccinated adults may now be rethinking their vaccination options.

“All Ontarians should ensure themselves, and their children, are up to date on their vaccinations,” the Ontario Ministry of Health said. “One dose of a measles-containing vaccine given after 12 months of age is up to 95 per cent effective at preventing measles. Having two doses is about 99 per cent effective.”

This isn’t the first time health officials have raised concerns over measles in Canada. There was a spike of 752 cases reported nationwide in 2011, and 418 cases in 2014.

Global concerns were also raised by the World Health Organization in 2023, after measles increases were noted in Europe, following a lapse in overall vaccinations due to the COVID-19 outbreak.

What if my child has only had one dose?

If you have been following the province’s vaccination schedule, and your preschooler has only had one MMR dose so far, it’s best to consult with your health-care provider if you have concerns.

“Children one to four years old who have received their first dose should receive a second dose as soon as possible, at a minimum of four weeks from the first dose,” the Ministry of Health said.

In Canada, the measles vaccine is only available in combination with the mumps and rubella vaccine or mumps, rubella and varicella vaccine. In some other countries, the measles vaccine alone is given.

For more information about the vaccine, visit .