What to know about switching brands when it's time for your booster.

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If you've been fully vaccinated against COVID-19, is it OK to switch to a different manufacturer's product for your booster dose? If you ask the US Food & Drug Administration (FDA), the answer is yes. Under a newly announced "mix-and-match" strategy, people who got a Pfizer, Moderna, or Johnson & Johnson (J&J)/Janssen COVID vaccine may switch to another brand's booster.

After reviewing available data, the FDA concluded that "the known and potential benefits" of using a single mix-and-match, or "heterologous," booster dose outweigh "the known and potential risks' in people eligible for boosters.

The US Centers for Disease Control and Prevention (CDC) has yet to revise its guidance. The CDC's Advisory Council on Immunization Practices is slated to hear a presentation on mix-and-match data during its October 21 meeting.

So if you're looking for a booster dose, what should you do? Here's the latest on the FDA's mix-and-match approach.

Why mix and match COVID vaccines?

Mixing vaccines has a couple of advantages. From a practical standpoint, the ability to switch from one manufacturer's vaccine to another gives Americans more flexibility when they go to the doctor's office or a pharmacy for a booster shot: No Pfizer in stock? Get the Moderna. Or so the thinking goes.

"This is going to give them some of that flexibility to go ahead and get boosted with what is convenient, whether that's what their physician might have in their office or what the local health department or vaccine clinics may have," Eric Adkins, MD, a professor of emergency medicine and critical care at the Ohio State University Wexner Medical Center, tells Health.

It would also extend an opportunity for people who received the one-dose J&J vaccine to "boost" with one of the mRNA (Moderna of Pfizer) vaccines if they so choose. A recent CDC study examined "real world" data from mid-March through mid-August on COVID vaccine effectiveness. The two-dose Moderna and Pfizer regimens were 93% and 88% effective, respectively, against COVID hospitalization, the study found, while the single-dose J&J vaccine had a lower level of protection, at 71%.

There's some thought that mixing vaccines might provoke a more powerful immune response. That's partly based on results of a small, pre-print study (not yet peer reviewed) on mix-and-match booster vaccination. Nine groups of about 50 people each participated in the study. Adults who had received one of the three COVID vaccines cleared for use in the US—Moderna, Pfizer, or J&J—were then given a booster of one of those three same vaccines.

Preliminary findings indicate that mixing and matching, regardless of the combination of vaccines and boosters, increased antibody levels, according to the New York Times. Of particular note were the results for J&J vaccine recipients: switching to a Pfizer booster resulted in a 35-fold increase in antibody levels, while those who got a Moderna booster had a 76-fold rise in antibodies. But the study has limitations, including its small size and short follow-up period, which may not capture rare side effects.

FDA Mix-and-match vaccine boosters
Credit: Alex Sandoval

How would mixing and matching work, exactly?

Each of the COVID-19 vaccines may be given as a booster dose to eligible adults who've completed a different COVID vaccine. The FDA lays out a couple of scenarios.

Let's say you had J&J. If you're 18 or older, you could go with the J&J booster, or you could get a shot of Moderna (which, for booster purposes, is a half-dose) or a shot of Pfizer. In each case, you'll have to wait at least two months after getting the primary J&J shot.

If you got Moderna or Pfizer and you fall into one of the categories of people authorized to get a booster, you have a choice too. You can get the same brand, you can switch to the other mRNA option, or you get J&J. Regardless of which one you choose, you'll have to wait at least six months after you've completed the two-dose primary vaccine regimen.

Are boosters already approved for each of the COVID vaccines?

Pfizer's booster, previously cleared for use by the FDA, earned the CDC's stamp of approval in late September. And it could be a matter of hours or days before the CDC recommends boosters for Moderna and J&J, after the FDA decided to expand use of booster doses.

The amended emergency use authorizations, announced by FDA on October 20, allow for a single booster dose in eligible adults.

Specifically, the FDA determined that a J&J booster dose may be given to adults aged 18 and older at least two months after getting the single-dose vaccine. And certain Moderna recipients (those aged 65 and older and adults 18 to 64 who are at high-risk of severe COVID or live or work in risky settings) may be eligible for a Moderna booster at least six months after the two-dose primary vaccination.

The Pfizer booster is recommended for older Americans and certain older adults with underlying conditions at least six months after completing the two-dose vaccine. Other at-risk adults and people who work in high-risk jobs where they might be exposed to COVID may also get vaccinated.

Which booster should you choose?

Paul Goepfert, MD, director of the Alabama Vaccine Research Clinic at the University of Alabama at Birmingham, suspects that switching from one vaccine to another will be safe. But based on the data he's seen, "there's really no big advantage to mix-and-matching," he says.

Whichever booster you get, rest assured that vaccination is highly protective against severe disease and hospitalization.

"I think these vaccines are so fantastically good that you that you can do whatever you want, and it's going to work," says Dr. Goepfert.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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