Measles cases increase by 173 in Ontario, bringing outbreak’s total close to 1,800

Public Health nurse Lauri Bidinot demonstrates how to give a measles shot to a young girl at Southwestern Public Health in St. Thomas, Ont., on Tuesday, March 4, 2025. THE CANADIAN PRESS/Geoff Robins

TORONTO — Public Health Ontario says 173 more people have been infected with measles in the province over the past week, bringing the number of cases to 1,795 since the outbreak began last October.

“That’s 173 more cases than we want to see,” said Dr. Sarah Wilson, a public health physician at the agency.

Public Health Ontario’s weekly measles report, released Thursday, said the virus continues to spread primarily among people who have not been vaccinated.

“Ninety-five per cent of cases are either unimmunized or with unknown immunization history, and three-quarters of the outbreak cases are in young people under the age of 20, so measles (is) impacting babies, children and adolescents,” said Wilson.

The latest number of cases is “consistent” with the province’s measles reports over the last several weeks, she said, adding there were 10 more hospitalizations.

The report said a total of 129 people have required hospitalization throughout the outbreak, with 10 people admitted to intensive care.

Although new measles cases have been reported in a dozen public health units across the province, most cases are concentrated in “pockets of individuals and communities who are under vaccinated” in parts of southwestern Ontario, Wilson said.

The Southwestern Public Health unit, which includes Oxford County, Elgin County and St. Thomas, continues to be hardest hit, with 98 of the new cases, according to the report.

Huron Perth Public Health unit has reported 22 new cases, Grand Erie Public Health has reported 14 and Chatham-Kent Public Health has reported 10.

Earlier this month, two secondary schools in the Region of Waterloo each had a confirmed case of measles and closed temporarily.

Measles has emerged in several parts of Canada, including Alberta, which has had more than 500 cases since March.

This report by The Canadian Press was first published May 22, 2025.

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

Nicole Ireland, The Canadian Press