Difference in new COVID vaccines 'extremely small,' expert says

With a new respiratory virus season underway, many Albertans are wondering what steps to take to protect themselves against the latest strains of COVID-19.

Health Canada approved Moderna’s Spikevax vaccine on Sept. 12, an updated COVID-19 formulation that targets the Omicron XBB.1.5 subvariant. Pfizer’s updated mRNA vaccine is also under review in Canada and has already been given the green light by the U.S. Food and Drug Administration.

For people who have had only Pfizer shots so far, is there any benefit in waiting until that vaccine is available in Canada?

“Officially all the public health groups are calling the mRNA vaccines interchangeable. And I think that's totally appropriate, because any differences between them in effectiveness as a single booster would be extremely small,” said Dr. Lynora Saxinger, an infectious diseases physician at the University of Alberta.

“If anything, I don't think there would be any particular reason to stay with Team Pfizer or Team Moderna. And there might be a potential benefit, which would be theoretic, to switching it up,” Sanxinger said.

Data from past rounds of COVID vaccinations suggests having a Moderna aspect to whatever combination of vaccine you have had was potentially associated with a better response in the long term, Saxinger noted.

“It seems like giving slightly different immune targets might strengthen the response in a way.”

The National Advisory Committee on Immunization recommended all authorized age groups get an updated COVID vaccine dose this fall to stay protected.

“Vaccine protection decreases over time, which means many of us are due for another dose. Receiving a shot of the new formulation will help protect people against the variants circulating currently and expected to circulate through the fall and winter,” Health Canada’s chief medical adviser Dr. Supriya Sharma said when approval of the Moderna vaccine was announced.

With this round of vaccines, health officials have moved away from calling the shots "boosters." Instead, the updated vaccines have been likened to a seasonal flu shot which are regularly reformulated to stay effective against the evolving virus.

“I think most of the public health groups are also moving away from calling it a booster. They're basically saying it's not clear that there's going to be a regular schedule of how often you're going to need a COVID shot,” Saxinger said.

“It's the same delivery of a different kind of recipe, essentially. And that is very much like what we do with influenza, and we don't call influenza (shots) a booster.”

Alberta has lagged behind other provinces in vaccine coverage beyond the initial two doses. For people who have grown weary during the pandemic and stopped paying attention to COVID updates, the shift in language could be a useful reminder of the need to keep their immunizations current.

“It would be fair to say that people who were infected during the first part of 2022, which was a lot of people, that's really not as relevant to your immune response now, and the first two doses aren't as relevant to your immune response now,” Saxinger said.

“It's kind of a fresh situation, too, because the current circulating strains are all in the general family of Omicron, but they have changed a fair amount.”

For Albertans hoping to get the Moderna update, it is still unclear exactly when the shots will be offered in the province, though they are expected to be available this fall.

“Alberta Health continues to plan for the fall rollout of vaccines for the upcoming respiratory virus season," an Alberta Health spokesperson said. "We will inform Albertans when more information is available.”