Public health agencies are encouraging people who received a first dose of mpox vaccine over the last two years to make sure they get a second dose.
Many people at risk for mpox exposure got vaccinated in Canada beginning in spring 2022, when a global outbreak of the virus was declared, Canada's chief public health officer said in a recent interview with The Canadian Press.
But a lot of them never got a second dose, which is recommended at least 28 days after the first shot.
”Please get that second dose in order to have the strongest immunity,” said Dr. Theresa Tam.
The number of mpox cases dropped in 2023 but appear to be on the rise again in parts of Canada. As of Aug. 24, there have been 166 confirmed cases in Ontario this year, compared to only 33 cases last year, according to data posted online by Public Health Ontario.
Only 36 per cent of people who got one dose of the mpox vaccine, Imvamune, in Ontario got a second dose, the agency said.
The majority of the province's cases — 83 per cent — have been in Toronto this year, it said.
"Toronto Public Health (TPH) continues to provide access to mpox vaccination through TPH clinics and community health partner clinics," Dr. Rita Shahin, associate medical officer of health for the city of Toronto, said in an emailed statement.
"Eligible residents are encouraged to start or complete the two-dose vaccination series for the best protection," Shahin said.
People eligible for vaccination include men who have sex with men and have more than one partner; men who have sex with men who have gone to venues for sexual contact; people who work in those venues; and sex workers, regardless of gender.
So far, Canada has only seen one type of mpox, known as clade II, which is spread primarily through close contact, including sexual contact.
People can also get the virus when handling personal items used by an infected person, including towels, clothing and bedding or when sharing utensils, toothbrushes, razors, needles or sex toys, according to the Public Health Agency of Canada website.
Montreal, which had many cases in 2022, doesn't appear to be seeing the same rise as Toronto. Nine mpox cases have been confirmed so far in 2024, according to an emailed statement from the city's public health authority.
As of Aug. 14, 18,349 people in Montreal had received one dose of Imvamune, but only about half of them — 9,645 people — had received a second dose, the statement said.
The World Health Organization declared mpox a public health emergency of international concern on Aug. 14, partly driven by the increase of another type of mpox, known as clade I, in Congo and its spread outside that country.
No cases of clade I mpox have been detected in Canada, Tam said.
One likely reason some people did not get a second dose is that the shots weren't promoted when vaccinations began in the spring of 2022, said Dr. Darrell Tan, an infectious diseases specialist at St. Michael's Hospital in Toronto.
"We didn't know how big of an epidemic we were going to be facing. (And) the amount of vaccine that's available in the Canadian stockpile really is a national secret because the initial purpose of stockpiling the vaccine was actually for bioterrorism preparedness rather than for traditional public health purposes,” Tan said in an interview.
"It was only some weeks to months later, (varying) by jurisdiction, that the kind of door opened to folks getting their second dose, and that's already going to be after the recommended 28-day window between doses for a lot of folks," he said.
In Toronto, for example, the first mpox vaccination clinic was on June 12, 2022, but the Ontario government didn't provide second doses until that October, a spokesperson for Toronto Public Health said in an email.
Tan said that in addition to providing second doses of the mpox vaccine to at-risk groups here in Canada, it's critical to make the vaccine available in Congo and other African countries that are hardest hit.
"If we prevent ongoing transmission of something in a different location ... not only is it the right thing to do morally, ethically, and from a public health perspective for the folks that could get that protection immediately, but there's a downstream impact (in Canada)," he said.
"The passage (of the virus) becomes less likely to make it over to our locations."
