Why the FDA’s ruling on mixing and matching vaccines will help more people get boosters

October 21, 2021, 8:18 PM UTC

Hi readers,

It’s been a busy week for the FDA, and the country’s vaccination drive is about to get even busier. On Wednesday, the FDA authorized boosters for the Moderna and Johnson & Johnson vaccines as well as the much-discussed “mix-and-match” approach, which allows people to get a booster shot of a vaccine that’s different from their initial dose. The move brings a confusing—and at times heated—debate over booster shots in the U.S. closer to its end. 

With signoff from CDC director Rochelle Walensky, which is expected to come after a CDC advisory panel meets today, the booster shot plan that the Biden administration introduced on August 18 can finally roll out in earnest. The plan has been controversial from the very start, in part because of the dubious ethics of administering them when so many around the world haven’t received a single dose—a fair and valid point that hasn’t been resolved. Vaccine inequity, as we discussed last week, is a serious issue around the world as well as within our borders. At the very least, the U.S. booster shot plan—in particular the authorization of the mix-and-match approach—will improve access to boosters for many Americans by allowing for more flexibility.

Permitting a mix-and-match approach increases access in three key ways: it allows people to get any booster that’s readily available to them, lets them choose which one they get, and reduces uncertainty about safety and efficacy. 

If everyone had to get a booster that matched their initial dose, their ability to get it would be limited by where they live (which in turn is limited by socioeconomic factors including race, income, and education), what the HHS makes available, and what their state health department requests. Permitting mixing and matching mostly mitigates these limitations, allowing for a faster and more widespread rollout.

People can now also choose their booster, which could also lead to more people getting an additional shot. A person may want one vaccine over another for a variety of reasons, including concerns about allergic reactions or increased risk of rare medical conditions associated with a certain vaccine. For example, Leana Wen, an emergency physician and public health professor at George Washington University, shared that she opted for a Pfizer booster even though she had initially received the Johnson & Johnson shot because the latter is linked to an extremely rare but serious blood clotting disorder in women under age 50. (It bears repeating, though, that all of the COVID vaccines have been deemed safe and effective, and the two health issues associated with the Johnson and Johnson vaccine are very rare.) As others have pointed out, the mix-and-match approach may reduce the appeal of the Johnson & Johnson vaccine, which has been shown to be less protective than Pfizer’s or Moderna’s. 

Perhaps the most salient impact of the authorization is clarity. Americans were already mixing and matching boosters, deliberately or not, regardless of the lack of guidance, as former FDA commissioner Scott Gottlieb pointed out to Fortune last month. “In a big country,” he said, “there are absolutely people who had Moderna who are getting Pfizer, and people who had Pfizer who are getting Moderna because they’re not keeping track well.” Authorizing this approach eliminates any uncertainty about whether doing so is safe and effective, which is a refreshing change of pace from the confusion of the last two months.

All that said, the booster rollout isn’t going to be easy. In fact, as STAT has noted, it’s probably going to be really hard. FDA authorization for each shot comes with very specific caveats: Pfizer and Moderna boosters are available only to older people and certain groups, but Moderna’s shot is a half-dose. Immunocompromised people, however, get a full dose of either. Meanwhile, the Johnson & Johnson booster is available to anyone over age 18 who initially got that vaccine, regardless of medical conditions, and the timing of that booster is different from that of the other vaccines. The CDC will get the final say on how this policy ultimately rolls out.

Chaotic as the booster shot debate has been, it boils down to this: Most vaccinated Americans will be able to get the booster they can access or want. The hope is that this means that more of the population will get additional protection sooner. We’re going to need it as we head into yet another winter of the pandemic.

Thanks for reading, and please reach out if you have any questions or comments—I’d love to hear from you.

Stay safe out there,




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