Measles outbreak declared in southwestern Ontario

Public health officials said they are now dealing with a measles outbreak in southwestern Ontario, with 19 confirmed cases as of Jan. 29.

Southwestern Public Health, which covers Oxford County, Elgin County and the City of St. Thomas, is reporting three cases of the highly contagious disease in children.

The remaining 16 infections are with Grand Erie Public Health, which serves the City of Brantford, Brant County, Haldimand County and Norfolk County. In an update Friday, officials said thirteen children and three adults have measles.

“When this started, we were looking at this being just a cluster of cases that were occurring predominantly in a non-immunized group,” explained Dr. Malcolm Lock, the acting medical officer of health for Grand Erie Public Health. “We’ve now moved to calling it an outbreak because of the numbers that are very rapidly increasing and the numbers that we think are going to continue to increase.”

He said the main concern with measles is how quickly it can spread.

“If we had [a sick person] in an unimmunized or susceptible group, they are potentially going to infect 12 to 18 people,” Lock explained. “I can’t emphasize more the contagiousness of this disease.”

Under vaccinated community

The outbreak in southwestern Ontario, said both health units, is linked to a specific community.

“This is in a population that does not support vaccination,” Lock said, clarifying that the people are predominantly unvaccinated or under vaccinated.

That has presented a significant problem in terms of tracking infections.

Grand Erie Public Health said once they are aware of a measles case, they can check the provincial database to investigate the person’s vaccination status.

“We don’t have any specific information mainly because there are groups in that area that do not support vaccination,” Lock explained. “Therefore, it’s very difficult to get an estimate on the number of those people that we have that are unvaccinated.”

Another complication is that the children go to a private school and can choose not to cooperate with public health.

“Sometimes that information is difficult to get from the schools,” Lock explained. “They are reluctant to release that. I can understand that because it can be a personal information issue, and a [Personal Health Information Protection Act] issue, that they don’t want to release it. Without that information though, there’s no way that we have to adequately check the contacts of any cases that occur, particularly in the schools.”

Grand Erie Public Health said they have shared information on measles and vaccinations with schools and churches in the community on multiple occasions, as well as material that can be shared with parents.

“That is about as much as we can do from a legal perspective,” Lock added.

Rise in measles cases

According to Public Health Ontario, 65 measles infections were reported across the province between January 2024 and January 2025. They included 39 confirmed and 26 probable cases. The illnesses were also spread out across 11 different public health units.

The data from Ontario’s integrated Public Health Information System, which was last updated on Jan. 15, showed five infections with Grand Erie Public Health (which took over for the Brant County Health Unit and Haldimand-Norfolk Health Unit in 2025) and 26 with Southwestern Public Health. It also showed a total of eight hospitalizations and one death due to measles.

Measles has been on an upward trend in the province since 2023, which Public Health Ontario said is in line with an increase in global cases of the disease.

Vaccination safety

Dr. Ninh Tran, the medical officer of health for Southwestern Public Health, called the measles vaccine “really safe and effective.”

Its efficacy, he added, is much higher than some other shots.

“I think the only effective method of preventing this disease is by vaccination,” Lock said. “Complications to measles in young children is fairly uncommon and rare, or has been up until now. I think that if we can prevent one serious illness, or even one death, from a child by vaccinating the population, [we should try] to get as near to herd the immunity status as we can.”

If enough people get vaccinated, he explained, vulnerable populations will have an even lower risk of catching the disease.

“It’s important that people realize that if they choose not to be vaccinated, and increase their susceptibility to these childhood diseases, I think they’re putting children at risk,” Lock stated.

He said efforts to vaccinate a majority of the population were so effective that, for some, it’s not a priority.

“They haven’t seen these illnesses and, of course, we haven’t seen the complications,” Lock explained. “Those complications still exist, rare though they may be, but they can be significant and lead to serious, life-long illnesses.”

“We have a lot of work to do”

Lock admits local health units are facing an uphill battle.

“My concern is that we have seen, as everyone is aware I’m sure, the uptake of vaccines, in general, has been falling off, rather than increasing,” he said on Wednesday. “We, public health, have a lot of work to do. Because I believe that people, the people that support non-vaccines or anti-vaccines groups, are sending out far more messages, probably, than we are.”

Lock said that is key to addressing current and future problems.

“I think public health needs to improve our messaging and try to find out what is the reasoning behind… younger people not achieving vaccine status and refusing vaccines. One can certainly assume that if that trend continues, we are going to see an increased number of not only measles, but other problems associated with vaccine prevention. Not the least of which, of course, is polio.”

New locations of exposure

Grand Erie Public Health recently shared a number of locations where the public may have been exposed to the measles virus, including restaurants and hospitals.

This week, they added three more locations to the list:

• Bethel Baptist School in Simcoe – From Jan. 20 and Jan. 21 between 8 a.m. and 5 p.m.
• Grey Gretzky Medical Centre in Brantford – On Jan. 22 between 10:45 a.m. and 2:45 p.m.
• Walsingham Christian School in Walsingham – From Jan. 21 to Jan. 23 between 8 a.m. and 5 p.m.

Symptoms of measles

The most common symptoms of measles are a fever, cough, runny nose and red and watery eyes. A rash, which will look like red spots with blotchy patches, will start on the face and then spread down the body to the arms and legs.

One reason measles is so highly contagious is that it is an airborne disease that can hang around in the air up to two hours after an infected person has left. Anyone with the illness is also contagious four days before, and up to four days after, the rash appears.

Symptoms usually start anytime between 7 and 21 days after exposure.

Anyone who suspects they have been exposed to the measles is asked to take extra precautions.

“They should really stay home and avoid high-risk settings,” advised Lock. “That would be doctor’s offices, childcare facilities, hospital emergency rooms, etc.”

Officials recommend getting two MMR (Measles, Mumps and Rubella) vaccines.

“Even with one dose, which may give up to 85 per cent immunity,” Lock said. “And with two doses, we consider that 100 per cent immunity.”