Confused about mix-and-match COVID vaccine boosters? Here’s what you need to know

Millions of people in the U.S. can now mix-and-match COVID-19 vaccines for their booster shot, which is optional. This means the vaccine you get for your booster can differ from the one you received for your initial doses.

The U.S. Food and Drug Administration authorized mixing-and-matching booster doses on Oct. 20, as well as booster shots of the Moderna and Johnson & Johnson vaccines for certain people. Late Oct. 21, the Centers for Disease Control and Prevention endorsed the recommendations, giving the green light for millions to roll up their sleeves a third, or second, time.

Pfizer booster shots have been authorized for certain people since September. And people with weakened immune systems have been allowed to receive a booster of either the Pfizer or Moderna coronavirus vaccines since August.

Scientists and doctors with the FDA determined the “known and potential benefits” of mixing vaccines for booster shots “outweigh the known and potential risks.”

They based their conclusions on a National Institutes of Health study that tested how different booster shot combinations of the three available COVID-19 vaccines influenced antibody levels. The study has yet to be published in a peer-reviewed journal.

It’s important to note antibody levels don’t reveal everything there is to know about protection against a disease, including COVID-19. There are other components of the immune system that play similar roles to antibodies. Studies on other pathogens suggest higher antibody levels equal greater protection, but scientists are still learning whether this is true of COVID-19.

Here’s what to know about mixing-and-matching COVID-19 vaccines for your booster shot.

Is it better to mix-and-match COVID-19 vaccines for booster shots?

Booster shots will make your arsenal of coronavirus antibodies grow, regardless of whether you mix-and-match. But some combinations appear to offer a bigger boost than others, according to the NIH study.

Still, experts aren’t deeming one booster option (getting the same vaccine) is better than the other (mixing vaccines.)

“I don’t think there are any losers here,” Kathryn Edwards, a professor of pediatrics at Vanderbilt University Medical Center in Tennessee who studies vaccines, told The Wall Street Journal. “Whether you get the same vaccine or a different one, it’s going to boost your immune response.”

However, people who initially received the J&J vaccine may be an exception.

Which is the best booster if you got the J&J shot?

The NIH study, which included 458 people, found that the one combination that produced the lowest levels of antibodies was a primary shot and booster of the J&J vaccine. This pairing led to a fourfold increase in antibodies.

A better combo was a primary J&J shot with a Pfizer booster, which triggered a 35-fold increase in antibodies.

The combination that led to the largest spike in antibody production was a primary shot of the J&J vaccine with a Moderna booster, which increased antibodies 76-fold.

“Having antibody levels that are higher are probably associated with longer duration of protection,” Edwards told the Journal. “So I think that a lot of people that got Johnson & Johnson initially may decide they’re going to get” the Pfizer or Moderna vaccines for their booster.

The J&J vaccine booster is the same dose as the first shot.

Anyone ages 18 and older can get the J&J booster shot — or a booster of the Pfizer or Moderna vaccines — at least two months after receiving their first dose.

Which is the best booster if you got the Moderna shot?

If you received the Moderna vaccine for your first two doses, the NIH study suggests you will gain the most antibodies if you receive a booster of the same shot.

Your next best option is to receive a Pfizer booster. If you choose to get a J&J booster, you will still benefit from increased antibody levels.

Moderna boosters are half the dose of the first two shots — 50 micrograms instead of 100 micrograms. So, regardless of what vaccine you got for your primary vaccination series, your Moderna booster will always be the half dose.

Company officials told The Associated Press they chose a lower dose because it led to fewer side effects and “leaves more vaccine available for the global supply.”

You are eligible for a Moderna booster shot if you’re 65 and older and if you’re ages 18 and older either at high risk for severe COVID-19 due to underlying health conditions or workplace exposure. You must wait at least six months after you receive your first two doses to get your preferred booster.

Which is the best booster if you got the Pfizer shot?

The NIH study shows people who got the Pfizer vaccine for their first two doses saw the biggest increases in antibody levels from a Moderna booster.

Getting a booster shot of the Pfizer or J&J vaccines will still spur your body to create additional coronavirus antibodies.

You are eligible for a Pfizer booster shot if you’re 65 and older and if you’re ages 18 and older either at high risk for severe COVID-19 due to underlying health conditions or workplace exposure. You must wait at least six months after you receive your first two doses to get your preferred booster.

The Pfizer vaccine booster is the same dose as the first two shots.

What are the side effects of a COVID-19 vaccine booster?

Data shows side effects after a booster shot are similar to those felt after your first dose of the J&J vaccine and after your second dose of the Pfizer or Moderna vaccines.

The most common side effects reported in the NIH study were injection site arm pain, headache, fatigue, muscle aches and chills.

The FDA found that swollen lymph nodes under the vaccinated arm were reported more frequently after a Moderna booster compared to the first two doses of the same shot.

Do you need a booster to be fully vaccinated against COVID-19?

No.

You are considered fully vaccinated two weeks after your second dose of the Pfizer and Moderna vaccines and two weeks after your single dose of the J&J shot.

You do not need a booster dose to be considered fully vaccinated against COVID-19.