Public health doctors and immunologists in Canada are calling for a wait-and-see approach as the idea of mixing doses of different COVID-19 vaccines is being considered to quickly inoculate more people around the world.
The changes will be guided by the results of a major study expected to be released this summer in the United Kingdom.
Kelly McNagny, an immunologist at the University of British Columbia, said mixing and matching vaccines is a viable way to proceed because mRNA vaccines from Pfizer-BioNTech and Moderna work essentially the same way as viral-vector vaccines manufactured by Oxford-AstraZeneca and Johnson & Johnson in creating a protein that triggers an immune response against the virus that causes COVID-19.
"I can't see a reason why mixing and matching would not work just fine, but the studies are not in yet," said McNagny, a professor in the school of biomedical engineering and the department of medical genetics.
"It is an evolving situation. There is great data to show that if you get the normally scheduled routine vaccination, you get protected really well. The problem is there's a shortage of vaccines."
Canada's chief public health officer, Dr. Theresa Tam, told a news conference this week that the mix-and-match data coming out of the U.K. is being followed "very closely" and that using different vaccines for the first and second doses may provide even greater protection.
Tam's comment came after the National Advisory Committee on Immunization said the Pfizer and Moderna vaccines are preferred over AstraZeneca and J&J due to a very low risk of blood clots, fuelling concern and confusion because the panel's recommendation contradicts Health Canada's position.
Further clarification is expected on whether people who received AstraZeneca for their first dose should also get the same vaccine for their second shot, Tam said.
“I think we’re all interested in the approach of actually mixing different types of vaccines, like an mRNA following a viral-vector vaccine, for example,” she said.
The U.K. mix-and-match study began in February with about 800 volunteers over the age of 50 who received either the AstraZeneca vaccine and then the Pfizer vaccine or vice versa several weeks later, or two doses of the same vaccine each time.
Participants, who did not know which vaccines they got, provided blood samples to measure the level of antibodies and T cells that vaccines produce to attack the virus.
British Columbia's provincial health officer, Dr. Bonnie Henry, said the study to determine the efficacy of administering different vaccines is among others being followed in Canada.
However, she and her colleagues across the country are advising everyone to get the first vaccine that's available to reduce transmission of COVID-19, Henry said, adding: "That includes the AstraZeneca vaccine."
Gurpreet Malhotra, CEO of Indus Community Services based in Mississauga, Ont., said the agency serving the South Asian community in the Peel region has worked hard to build vaccine confidence and any kind of mixed messaging about a possible mix-and-match plan could be rejected because people may wait for a specific vaccine in keeping with the national panel's recommendation.
Poor communication about COVID-19 vaccines has caused "a significant portion of the population to freak," especially those who are already hesitant about getting vaccinated in any community across the country, he said.
"Some of those are high-risk groups. Those people need their confidence built and every time there's a confusing message, that creates another opportunity to say, 'Let's wait and see,'" he said.
Several social service groups in the Peel area, home to a large number of essential-service jobs at warehouses and food processing plants, have been educating people in multiple languages to create a strong vaccination program for those more vulnerable to infection, Malhotra said.
"The community is now actively mobilizing at its temples and pop-ups and mosques and other community settings. There's not a situation where there's vaccine waiting to go into someone's arm."
He urged federal and provincial officials to provide streamlined information and said the national immunization panel's position on the AstraZeneca vaccine only served to create mistrust among those who are now confused about whether they should wait for a different vaccine for their second dose.
"Mixed messaging is not helpful. And having contradictory messaging or messaging that gets walked back after consideration doesn't help."
This report by The Canadian Press was first published May 5, 2021.
Camille Bains, The Canadian Press