Ontario sees sharpest rise in measles yet with 223 new infections since last week

Courtesy Barrie360.com and Canadian Press

By Hannah Alberga, May 1, 2025

Ontario is reporting its highest increase in measles cases since its outbreak began, with 223 new infections in the province over the past week.

That brings the total number of people in the province who have fallen ill from the virus to 1,243 since October. 

Public Health Ontario said in a report today that 84 people have been hospitalized – including 63 children – during the course of this outbreak. Eight patients have been admitted to intensive care.

The agency notes that its southwestern public health unit has had 57 new infections, compared to 15 the previous the week. Neighbouring Grand Erie Public Health is also seeing an uptick with 46 cases, compared to two the previous week.

Southwestern Public Health Unit’s Dr. Ninh Tran said this “sharp rise” is due to exposures in large unvaccinated households between siblings and other family members, and places where unimmunized people gather.

He said the increase in cases is not tied to any “particular singular” event, but rather, it’s due to a group of cases linked to one another. However, he did not pin the spread to a particular group.

Tran said the duration of hospital stays on average is usually just over three days, and ranges from about one to 11 days. 

Alberta reported 170 measles cases Wednesday – including nine hospitalizations – since its outbreak began in March.

Alberta Medical Association president Dr. Shelley Duggan told The Canadian Press last week the numbers suggest that within weeks, that count could skyrocket to more than 1,000, like in Ontario. 

Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.

2) Transplant recipients and other immunocompromised people worry about measles exposure

Courtesy Barrie360.com and Canadian Press

By Hannah Alberga, April 29, 2025

Laurie Miller, a 59-year-old heart transplant patient exposed to measles in Stratford, Ont., says her story speaks to the risks people who are immunocompromised face during an outbreak. 

She brought her husband to the emergency room in mid-March after an all-terrain vehicle accident. Their local public health unit called a few days later saying a patient with measles had been in the emergency room too. 

Miller was at the hair salon she works at in a retirement home when she got the call. Though she’s born before 1970, a cohort Health Canada says likely acquired natural immunity to measles, the public health official told her to leave immediately and quarantine at home. 

Her public health unit Huron Perth has seen more than 120 cases since an outbreak began in October. Public Health Ontario said Thursday the total number of cases reported in the province has surpassed 1,000, with 95 new cases since last week. Alberta’s case count was 137 as of Friday, with the province noting 15 were “known to be communicable,” while Quebec declared its outbreak over earlier this week.

People who are immunocompromised cannot get immunized against measles because the vaccine contains a live attenuated virus, a weakened version of the virus that teaches the body how to fight the disease, because it could infect a weakened immune system. 

“There’s so many of us out there that are immunocompromised. It’s not just heart, it’s liver, it’s lung, it’s people that have cancer. They’re doing chemo. There’s people with heart failure,” Miller says. 

Dr. Deepali Kumar, director of the Ajmera Transplant Centre at Toronto’s University Health Network, says last time Ontario had a measles outbreak this big – before the disease was eliminated in Canada in 1988 – there were far fewer immunocompromised people. 

Research published in JAMA in February showed the rate of immunosuppression in 2021 was an estimated 6.6 per cent among adults in the United States, compared to 2.7 per cent in 2013. The paper says the increase may be due to an increase in immunosuppressive medications available to patients.

Similarly, Kumar estimates about four to six per cent of the Canadian population is immunocompromised to some degree in part because of medical advances in immunosuppressants. 

“We haven’t had so much measles circulating when we’ve had so many people that are immunocompromised,” Kumar says.

“It’s a bit of a new era.”

This new era has led researchers to re-examine how to protect this population. 

On March 14, the day after she was notified of exposure, Miller drove to Toronto General Hospital, as advised by the team of health providers who manage her care. She received an intravenous infusion of immunoglobulin therapy containing antibodies from donated human blood to provide immediate short-term protection against measles.

She hasn’t gotten sick, but given it’s one of the most contagious diseases in the world – one person with measles can infect nine out of 10 of their unvaccinated close contacts, according to the World Health Organization – she’s been cautious. 

At a crowded grocery store over the weekend, Miller says she left feeling uncomfortable.

“It does stop you from doing things,” she says. 

Kumar says she is concerned about immunocompromised people who are exposed, but don’t make it to a doctor in time, the way Miller did. She says there’s a six-day window post exposure that immunoglobulin can be given. 

“Measles is a virus that can attack many parts of the body, it can attack the lungs, the brain. And so in the most severe cases, and if you’re immunocompromised, then the chances of having the severe form of the virus increases,” says Kumar. 

For Steff Di Pardo, a 29-year-old Mississauga resident diagnosed with ankylosing spondylitis, a form of arthritis and autoimmune disease, that’s been a scary reality. 

The medical infusions she receives every eight weeks to manage chronic back and pelvic pain helps slow down the progression of the disease, but it also makes her immunocompromised. 

As a result, she says she’s always aware of her surroundings and wears a mask, but recently, that awareness has been heightened as measles has circulated. 

Janna Shapiro, a post-doctoral fellow at the Centre for Vaccine Preventable Diseases affiliated with the University of Toronto, is researching the risk of live vaccines for immunocompromised patients in the current climate of a measles resurgence. 

“That risk-benefit may be a little bit different than it was five or 10 years ago,” says Shapiro, suggesting the area deserves a re-examination. 

She’s trying to understand if the immune system of children with leukemia is strong enough to protect them from a weakened version of the virus in the vaccine. Shapiro is also looking at other groups, such as kids treated with a new group of drugs called biologics for inflammatory bowel disease, that she says didn’t exist or did not exist to this scale before measles was eliminated in Canada. 

“We’re trying to understand this and understand how to strategize and best use vaccines as well as other tools to protect these kids. But the reality is that if everybody around them is immunized, then they’re much less likely to be exposed.”

Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.