Ontario measles cases rising this year
Ontario has recorded 14 measles cases so far in 2024 — twice as many as all of last year, according to Public Health Ontario.
Eight cases were in children and six in adults, with all but one of the 14 cases acquiring a measles infection while travelling outside Canada, the agency’s most recent surveillance report shows. The single case not linked to travel — a man in his 30s in York Region — didn’t know he got infected, prompting health officials at the time to suggest he had been infected within the community.
The report shows that of the eight children with measles, six were unvaccinated, while two had unknown immunization status. One adult case was unimmunized, two adults had unknown immunization status and three had previously received at least two doses of a measles vaccine.
A two-dose series of the measlesmumps-rubella (MMR) vaccine or the measles-mumps-rubella-varicella (MMRV) vaccine will protect up to 99 per cent of people against the disease, among the most contagious infections in the world. People without immunity, from either immunization or a previous infection, have up to a 90 per cent chance of getting infected after being exposed to the virus.
Shelly Bolotin, director of the Centre for Vaccine Preventable Diseases at the University of Toronto’s Dalla Lana School of Public Health, said in an email that while the measles vaccine is very effective, “nothing is 100 per cent.”
“So occasionally we do get cases in individuals who have been vaccinated with two vaccine doses. These cases often experience a milder course of illness and are thought to be less likely to transmit measles to others.”
As of April 24, measles has been reported in nine of Ontario’s 34 public health units, including two cases in Hamilton and five cases in Toronto. Last year, Toronto recorded four cases of measles, up from one case in 2022.
So far, no secondary measles infections have been reported in the province, according to the new report, which showed 782 people were tested for measles between Jan. 1 and April 20.
Ontario’s most recent confirmed measles case — a child with a recent history of international travel — was reported in Hamilton on April 17. Dr. Brendan Lew, associate medical officer of health, said in an email that once the case was confirmed, public health started an investigation and “rapidly mobilized” its workforce to identify exposure settings and reach out to the case’s contacts “to assess risk and provide guidance and education.”
“There is not known to be settings in the public where unidentified contacts were exposed following Hamilton Public Health Services’ thorough investigation,” Lew said, noting the health unit held two measles-specific vaccine clinics for at-risk contacts.
The Star has so far tracked 66 cases of measles nationwide, more than five times as many cases as all of 2023. The majority of infections are in Quebec, which has reported 49 cases as of Friday, according to the provincial health authority.
On Wednesday, Alberta Health Services confirmed an person with measles went to multiple places in Edmonton while infectious, including Edmonton International Airport and the Stollery Children’s Hospital Emergency Department.
Eight cases were in children and six in adults, with all but one of the 14 cases acquiring a measles infection while travelling outside Canada