Nearly 200 cases of measles have been reported in Ontario in the past two weeks alone, twice as many as in the entire decade between 2013 and 2023, as a major multijurisdictional outbreak balloons in Southwestern Ontario.
Most of the cases have been identified in unvaccinated children in the Grand Erie and Southwestern public-health units, which cover neighbouring regions that hug the shore of Lake Erie, south of London.
However, a new surveillance report from Public Health Ontario, released Thursday, shows measles is also spreading well beyond the epicentre of the outbreak. Seven additional health units have identified cases of measles since Feb. 27, when PHO last published an update on an outbreak that began last October with an infected traveller bringing the virus to Ontario from New Brunswick.
In Ontario, “we certainly haven’t seen this number of cases since before measles was considered eliminated from Canada. That was in 1998,” said Christine Navarro, a public-health physician with the provincial agency.
Measles is making a comeback in Canada, the United States and other Western countries that have officially eliminated it, after enthusiasm for – and access to – vaccines waned during the COVID-19 pandemic.
In Texas and New Mexico, two people recently died of measles-related complications after they were infected during a large outbreak rooted in Mennonite communities that shy away from vaccines.
New Brunswick, meanwhile, saw a significant measles outbreak last fall that began with a case brought in from abroad. The virus spread from New Brunswick to Ontario, touching off the current outbreak in Canada’s most populous province. Quebec, Manitoba and British Columbia have also reported measles cases this year.
Seeing unvaccinated children fall seriously ill with measles has been “tear-jerking for me as a pediatric infectious-disease doc and also as someone coming from the developing world,” said Michelle Barton-Forbes, the division chief of infectious diseases at London Children’s Hospital, where 15 children have been admitted for treatment of measles-related complications.
Dr. Barton-Forbes is originally from Jamaica, where, in the past, people who wanted vaccines couldn’t necessarily afford or access them. In Canada, she said, “we’re seeing different groups choose not to have vaccines for a spectrum of reasons, from religious straight across to just personal choice or fear and anxiety.”
Many of them have never witnessed “the ugly face of vaccine-preventable diseases,” she added.
In Ontario, a total of 372 cases in 11 public-health units – stretching from Windsor to Niagara to North Bay – have now been linked to the outbreak. In the past two weeks, 195 cases have been identified. There were only 101 cases of measles reported in Ontario between 2013 and 2023.
Thirty-one Ontarians sick with measles have been admitted to hospital for treatment, 30 of whom were unimmunized and 27 of whom are children. One child required intensive care, the PHO report said.
Southwestern Public Health, which serves the cities of St. Thomas and Woodstock and several nearby towns, including Tillsonburg, Aylmer and Ingersoll, has reported 183 cases of measles since the outbreak began, according to PHO. Seventeen patients were sick enough to be admitted to hospital.
“What we’re seeing now is like nothing we’ve ever seen before, at least during my professional career,” said Ninh Tran, medical officer of health for the Southwestern Public Health Unit.
Dr. Tran added that although the numbers are “jarring,” he thinks many more cases are going undetected as patients recover at home without contacting a doctor or visiting a health care facility.
Like West Texas and New Mexico, this region of Ontario has a large Mennonite community. Public-health authorities have not released any information suggesting that the current outbreak is connected to the Mennonite community, although there have been a handful of measles exposure notices at Mennonite schools. Dr. Tran declined to comment on the matter.
In the neighbouring Grand Erie Public Health Unit, 100 cases of measles have been reported since the start of the outbreak, according to PHO’s figures.
The number of measles cases recorded in Canada so far this year has already eclipsed the annual total for any year since 2014, when 418 cases were reported, most associated with an outbreak in a religious community in British Columbia that eschewed vaccines.
The most recent national surveillance report, which includes data up to March 1, said there have already been 224 measles cases in Canada in 2025. The tally has grown substantially since then, as Ontario’s new report demonstrates.
There were 147 cases of measles identified countrywide last year, the most since before COVID-19 struck, according to the Public Health Agency of Canada.
Measles is one of the most contagious viruses on the planet. It can linger in the air for up to two hours after a contagious person leaves a room. Symptoms start with a fever, lethargy, cough and red and runny eyes, then progress to a telltale blotchy red rash.
The infection is fatal in rare cases. Last year, a child in Hamilton died of measles.