Results from a UW Medicine COVID-19 vaccine mix-and-match study were reviewed by a Centers for Disease Control and Prevention (CDC) panel ahead of the group’s decision to authorize mixing and matching of booster shots late last month.
“[The] data that we have today shows that it is safe, and also effective at creating a strong immune response,” said Dr. Christine Johnston, associate professor of medicine, Division of Allergy and Infectious Diseases at the University of Washington School of Medicine. “We’re still studying this, but at this point, we’re seeing that this is a safe option.”
On Oct. 20, the Food and Drug Administration authorized expanding the U.S. booster campaign, which began with extra doses of the Pfizer vaccine in September.
Tens of millions of Americans are now eligible for boosters and formally allow “mixing and matching” of shots—making it simpler to get another dose, especially for people who had a side effect from one brand but still want the proven protection of vaccination.
In the UW study, Johnston said each possible initial vaccine series has been combined with an alternative booster (either Pfizer, Moderna, or Johnson & Johnson vaccines) and monitored through the study. No adverse effects have been observed, beyond occasional soreness or fatigue associated with the original doses. UW Medicine is one of 10 sites performing the study, which is sponsored by the National Institutes of Health.
“The mix and match strategy in particular does give people a lot of options,” Johnston said. “There was a preliminary study, preliminary results presented that showed that doing a booster of any type really does increase the immune response, no matter what primary vaccine series you received. That means that really, you can receive any booster, and be confident that you’re going to get a strong response.”
While boosters are now authorized for all three types of vaccines available in the United States, there are differences between their doses. Pfizer and Johnson & Johnson boosters are full doses equal to their original series, while the CDC found that the Moderna booster shot provided ample protection as a half-dose compared to its initial series.
FDA officials said they wanted to make the booster guidance as flexible as possible, given that many people don’t remember which brand of vaccine they received.
“Being able to interchange these vaccines is a good thing—it’s like what we do with flu vaccines,” FDA’s Dr. Peter Marks said. “Most people don’t know what brand of flu vaccine they received.”
This health series is made possible by funding from the Washington State Department of Health, which has no editorial input or oversight of this content.