Ontario Health says mixing vaccines is safe after WHO chief scientist comments

Health officials are reassuring Ontarians that mixing COVID-19 vaccines is safe and effective against the virus, following some confusion about messaging from the World Health Organization that seemed to say there is not enough data on the practice yet.

At the WHO’s Monday coronavirus briefing, chief scientist Dr. Soumya Swaminathan warned against mixing vaccines, as part of a longer discussion about booster doses.

It was later clarified that she was referring to booster doses for fully vaccinated people and warned against individuals “vaccine shopping” outside of public health regulations or deciding for themselves about a third or fourth shot in countries where there is ample supply of vaccines. Rather, she said people should rely on public health agencies to make that decision based on available data.

On Tuesday, Ontario’s Associate Chief Medical Officer of Health, Dr. Barbara Yaffe attempted to clear up the confusion and said taking a combination of any of the two mRNA vaccines, Pfizer or Moderna, as well as taking an mRNA vaccine following the AstraZeneca shot is still being recommended in the province.

“We are following the advice of the National Advisory Committee on Immunization (NACI), which recommends it is safe to mix these vaccines, based on studies from the U.K., from Spain, from Germany,” she said. “They have found that mixing these vaccines is very safe and produces a strong, effective immune response.”

Dr. Yaffe added that Ontario Health will continue to follow studies and data closely and work with NACI as well as the federal government on the issue.

Chief Medical Officer of Health, Dr. Keiren Moore, once again reiterated the importance of getting fully vaccinated and warned that the Delta variant “will want to surge and return in September if not earlier,” as the risk of spread is heightened with indoor activities and cold weather.

“The Delta strain will seek out unvaccinated individuals and so becoming immunized as soon as possible will ensure that you are not on that path of least resistance for the virus,” he said, adding that the highest incidence of infection over the last three months have been seen among those who are unvaccinated.

Dr. Yaffe said that since it was declared a variant of concern, Ontario has had over 20 outbreaks where Delta was the dominant strain. They usually involved gatherings where people were in close contact, without a mask and had low vaccination rates. Over 88.6 per cent of the current COVID-19 cases in the province are from the Delta variant.

She said mixing of the vaccines will allow people to get both shots of the vaccine sooner and help stem the spread of the variant.

Note: This article was edited to better reflect the comments made by Dr. Soumya Swaminathan in the correct context.