Should You Mix and Match COVID Booster Shots? Top Boston Doctors Weigh in

More data is needed to have a complete understanding of the mix and match method's efficacy, top Boston doctors said, and gathering it could be tricky

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Federal regulators authorized a "mix and match" approach for COVID-19 booster shots this week, but is it a good idea for you?

Mixing and matching refers to giving a booster dose of a vaccine that is different from the type that was used for the initial vaccination series. For example, receiving the first two doses of Moderna vaccine and then getting a Pfizer booster.

The Food and Drug Administration on Wednesday signed off on extending COVID-19 boosters to Americans who got the Moderna or Johnson & Johnson vaccine and said anyone eligible for an extra dose can get a brand different from the one they received initially.

The decisions mark a big step toward expanding the U.S. booster campaign, which began with extra doses of the Pfizer vaccine last month. It was also endorsed Thursday by a CDC advisory panel.

The mix and match approach is intended to alleviate supply issues and provide flexibility for people who want to maintain protection against the coronavirus.

As part of the weekly "COVID Q&A" series, NBC10 Boston asked three top Boston doctors Tuesday about the risks of combining these vaccines.

Massachusetts health leaders are making moves to prepare for the distribution of new booster shots.

What are the benefits of mixing and matching vaccines?

Mixing and matching could alleviate supply issues, making it easier for people to get the booster shot.

"The flexibility could be really helpful," Dr. Shira Doron of Tufts Medical Center said. "Physicians have been recommending mix and match, even though it's not FDA approved, so it's important to really have that approval in place."

A highly anticipated study on mixing and matching COVID-19 vaccines found the approach to be safe and effective, though the Moderna and Pfizer-BioNTech vaccines were found to spark a stronger immune system response than Johnson & Johnson.

Despite the new data, many questions remain unanswered.

"I think we're actually in somewhat uncharted territory here," Dr. Daniel Kuritzkes of Brigham and Women's Hospital said.

"We don't really understand the implications," Boston Medical Center's Dr. Davidson Hamer added.

Millions more Americans will have access to booster shots for COVID-19 vaccines after the FDA and the CDC approved new measures.

How effective is the mix and match method?

The National Institutes of Health study, which was released last week and has yet to be peer reviewed, found that people who received the Johnson & Johnson vaccine produced stronger antibody levels after receiving a booster shot made by Moderna or Pfizer, compared to a booster from Johnson & Johnson.

But that study on the strategy looked at antibody levels.

"Those don't necessarily completely correlate with protection," Doron said. "I think the key is just to have flexibility for people to be able to have a conversation with their doctor and take whatever their physician recommends or what they prefer."

Those who were originally vaccinated with the Pfizer or Moderna vaccines and received either company's booster shot produced comparably strong immune responses, the researchers observed.

"It's not, to me, 100% clear that there's necessarily a clinical benefit to taking an mRNA vaccine after J&J, as opposed to taking the J&J vaccine," Doron said. "And the J&J vaccine is actually lasting a really long time without immunity waning, like the mRNA vaccines."

There is more work to be done to have a complete understanding of how effective this method is, experts said, and it likely won't be easy.

"We need more efficacy data -- really I would call it real-life effectiveness data -- to have some follow up over the next six to 12 months and get a feel for what the protection is," Hamer said. "Including in different combinations, which is going to be a little bit tricky to do if it's not being done systematically."

"It makes it complicated to do the effectiveness studies because you're going to have so many different combinations," Doron added, "but I think, ultimately, it's doable and we'll learn a lot from it."

What are the health risks of mixing and matching vaccines?

The risk of mixing vaccines is likely the same as sticking with one type of vaccine, Kuritzkes said, because they're all producing the same basic protein of the virus and generating similar immune responses.

"Personally, I don't think there's a risk beyond the intrinsic risk of each vaccine," he said. "I don't think there's a real risk of mixing the vaccines and there are -- although it's in hundreds not tens of thousands of people -- there are enough mixing studies now that suggest that it's perfectly safe to mix them."

"I agree," Hamer added. "We have a pretty good understanding now of the major common and some of the less common side effects for each of the vaccines."

The physicians named vaccine-associated myocarditis, inflammation of the heart muscle, as one of the major risks of getting the messenger RNA vaccines.

"But it's very, very rare," Hamer said. "And the risk of myocarditis is actually much higher if you get COVID-19 if you haven't been vaccinated."

The "most worrisome" side effect from the Johnson & Johnson vaccine is blood clotting, Hamer said, though he mentioned that is also rare.

"I don't anticipate that we're going to see surprises, like new kinds of side effects coming up, when we go from Johnson & Johnson to the messenger RNA vaccine. We do need to watch for the kinds that we already know about and, of course, for new ones," Hamer said. "I don't anticipate, really any major surprises as we start mixing and matching vaccines."

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