2nd mpox vaccine dose still needed by Canadians at risk: public health

Public health agencies are urging individuals who received their first dose of the mpox vaccine over the past two years to ensure they complete their vaccination by getting the recommended second dose.

Beginning in the spring of 2022, many people in Canada at risk of mpox exposure were vaccinated after a global outbreak was declared, Canada's chief public health officer, Dr. Theresa Tam, said in an interview with The Canadian Press. However, many did not follow up with a second dose, which is recommended at least 28 days after the initial shot.

"Please get that second dose in order to have the strongest immunity," Dr. Tam advised.

Though mpox cases dropped in 2023, there has been a recent increase in parts of Canada. As of August 24, Ontario has reported 166 confirmed cases this year, compared to just 33 cases in 2022, according to data from Public Health Ontario. However, only 36 percent of those who received the first dose of the mpox vaccine, Imvamune, went on to get the second dose.

Most of Ontario’s cases—83 percent—have been concentrated in Toronto, said Public Health Ontario.

Dr. Rita Shahin, Toronto’s associate medical officer of health, stated in an email, "Toronto Public Health (TPH) continues to provide access to mpox vaccination through TPH clinics and community health partner clinics." She encouraged eligible residents to either begin or complete their two-dose vaccination series for optimal protection.

Eligibility for the vaccine includes men who have sex with men and have multiple partners, individuals who frequent venues for sexual contact, people who work in such venues, and sex workers of any gender.

To date, only one strain of mpox, clade II, has been detected in Canada. This strain primarily spreads through close contact, including sexual contact. The virus can also be transmitted through handling personal items used by an infected person, such as towels, clothing, and bedding, or by sharing utensils, razors, toothbrushes, needles, or sex toys, according to the Public Health Agency of Canada.

In contrast to Toronto, Montreal has seen fewer mpox cases this year, with only nine confirmed in 2024, according to the city’s public health authority. Of the 18,349 people in Montreal who received the first dose of Imvamune, only about half—9,645—went on to receive a second dose.

One possible explanation for the low uptake of second doses is that when vaccinations started in 2022, there was little promotion of the need for a follow-up shot, 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," Tan said. He also noted that the limited availability of vaccines from Canada’s stockpile, initially reserved for bioterrorism preparedness, delayed access to second doses in some regions.

For example, while Toronto’s first mpox vaccination clinic opened on June 12, 2022, the Ontario government didn’t start offering second doses until October.

Tan emphasized that, in addition to vaccinating at-risk groups in Canada, it’s crucial to distribute the vaccine in Congo and other African countries severely affected by the virus. "If we prevent ongoing transmission of something in a different location, it’s not only the right thing to do morally and ethically but also has a downstream impact on preventing the virus from reaching Canada," he said.