September 7, 2022 2:28 PM EDT

Health officials say it’s time for most Americans to get another booster dose—this time, with a new Omicron-specific shot made by either Pfizer-BioNTech (for people 12 and older) or Moderna (for adults 18 and older). But should you stick with the vaccine brand you’ve been using, or can you mix and match? Here’s what to know.

Mixing and matching booster doses is likely fine

Several COVID-19 vaccines have become available in the U.S. since the first shots were authorized at the end of 2020. Currently, two primary-series COVID-19 vaccines (made by Pfizer-BioNTech and Moderna) are approved by the U.S. Food and Drug Administration (FDA), and two (made by Johnson&Johnson-Janssen and Novavax) are authorized for emergency use. Shots from Pfizer-BioNTech and Moderna are approved as booster doses, and J&J’s booster is authorized for those who received that brand for their one-dose primary shot, or for those who cannot safely receive the other boosters because of the risk of side effects.

The U.S. Centers for Disease Control and Prevention (CDC) recommends that people not mix the two primary series doses of the mRNA vaccine—so if you’ve been vaccinated with Pfizer-BioNTech for your first dose, for example, your second dose should also be from Pfizer-BioNTech; the same goes for Moderna. But the abundance of options means you may have already received a booster dose from a different manufacturer, and that’s just fine. Studies have shown that people who received mRNA booster doses of the original vaccine made by a different manufacturer than that of the primary series generated similar virus-fighting antibodies against SARS-CoV-2, compared to people who got the same brand of primary and booster shot.

That was the case with the original vaccines and boosters. But human studies of the new Omicron boosters have not been completed yet—they will be launched in September—so there are no data yet on what happens when people who have been vaccinated with one company’s shots then get an Omicron booster made by a different company. It’s also not clear what happens, for instance, if someone who was vaccinated with Moderna’s shot, then boosted with Pfizer-BioNTech’s, now gets a Pfizer-BioNTech or Moderna Omicron booster.

But based on previous studies of mixing and matching, health officials are relatively confident that the booster doses are interchangeable, and the CDC says people over 18 “may get a different product for a booster than they got for their primary series, as long as it’s Pfizer-BioNTech or Moderna.”

One thing to keep in mind, however, is that all along, Moderna’s vaccine doses have been slightly higher than those from Pfizer-BioNTech. The same is true of Moderna’s new Omicron booster. A higher dose means that people getting Moderna’s Omicron booster may experience slightly higher rates of side effects, such as swelling, arm soreness, fever, and fatigue compared to people who get Pfizer-BioNTech’s. But it may potentially come with an advantage, if the experience with the original booster shots is any guide. Earlier studies involving people who received the original Moderna booster suggested that they generated higher levels of virus-fighting antibodies compared to people who received a Pfizer-BioNTech booster.

Can you mix and match booster doses for kids?

It depends on how old your child is and which vaccine they received as their primary series. Children ages 12 to 17 who were vaccinated with either Moderna’s or Pfizer-BioNTech’s shots as their primary series can get boosted with Pfizer-BioNTech’s new Omicron booster. Neither Omicron booster is authorized yet for children under 12—so those children will still receive a booster of the original vaccine (if they’re eligible to get boosted).

If your child was vaccinated with Moderna as a primary series, Moderna booster doses of any kind—original or Omicron-specific—have not been authorized for children six months to 11 years old yet. Children in this age group who were vaccinated with Moderna are not recommended to get a booster dose at this time. Children five to 11 years old who were vaccinated with Pfizer-BioNTech can only get an original vaccine booster, not the bivalent Omicron booster, made by Pfizer-BioNTech.

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