Can You Mix and Match COVID-19 Boosters?

Older woman getting a COVID-19 vaccine.

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Key Takeaways

  • Based on CDC guidance, you should get a COVID-19 booster from the same brand you received your initial vaccine.
  • There is not enough data to conclude that it's safe to mix COVID-19 boosters with different branded COVID-19 doses.
  • Because Pfizer and Moderna vaccines share the same safety and efficacy profiles, infectious disease experts do not expect that mixing booster shots will lead to bad side effects. 

Health officials recently recommended that most Americans get an additional dose of the mRNA COVID-19 vaccines. These boosters could become available in the coming weeks.

Currently, the Centers for Disease Control and Prevention (CDC) officially recommends sticking with the same vaccine brand you originally received when possible.

"For people who received either Pfizer-BioNTech or Moderna’s COVID-19 vaccine series, a third dose of the same mRNA vaccine should be used," the CDC states. "If the mRNA vaccine product given for the first two doses is not available or is unknown, either mRNA COVID-19 vaccine product may be administered."

But multiple reports show that people have taken matters into their own hands anyway. Some individuals report receiving an mRNA dose after previously receiving Johnson & Johnson. Others may have gotten a mix of Pfizer and Moderna doses. Verywell spoke to experts on whether mixing and matching your vaccine brands when receiving a booster is safe.

Can You Mix Booster Shots?

While data on boosters is limited, much of the understanding on dosing comes from lessons learned from the first and second doses of Pfizer and Moderna.

John Swartzberg, MD, FACP, clinical professor emeritus at UC Berkeley’s School of Public Health’s division of infectious diseases, tells Verywell that there isn't sufficient data to conclude that COVID-19 boosters can be mixed safely with different brands of COVID-19 vaccines.

According to Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo’s Jacobs School of Medicine and Biomedical Sciences, during the initial vaccine rollout, people mistakenly got Pfizer as their first shot and Moderna as the second without any extreme effects.

“So I don’t anticipate that there would be any issues from a safety point of view or an efficacy point of view in terms of crossing the two RNA platforms,” Russo says. 

The CDC currently recommends, that when a vaccine series becomes unavailable with the same brand, it's best to delay the following doses until the vaccine from the same brand becomes available.

So far, though, there have been no reported adverse effects from mixing brands for first and second doses, according to Swartzberg. “In people who’ve had Moderna, when you couldn’t get Pfizer, it’s been fine and vise versa,” Swartberg says.

It helps that both vaccines are messenger RNA vaccines. Although the makeup of both vaccines is proprietary, Russo suggests that the difference lies in their preparation in lipid nanoparticle coding—small balls of fat that prevent the mRNA from degrading.

“There may be differences in the liquid nanoparticle preparations between the two vaccines," Russo says. "But both of them have the same coding."

While it's not recommended, mixing brands when receiving a booster likely isn't dangerous. Russo and Swartzberg do not anticipate any safety issues from mixing brands. Overall, Pfizer and Moderna shots share similar safety profiles.

“They [Pfizer and Moderna shots] really have been in lockstep in terms of safety and efficacy,” Russo says.

What about Johnson & Johnson?

The CDC currently has no plans in place for recommending booster shots to those who received a Johnson & Johnson dose.

The company, however, did report that preliminary data shows their booster could increase immunity levels. So a Johnson & Johnson booster may be coming down the pipeline.

And there is some percent for mixing mRNA and Johnson & Johnson doses. For folks who experienced allergic reactions to any of the mRNA vaccines, a CDC scientist said that the Johnson & Johnson vaccine could potentially be used as a substitute as the second dose to complete immunity. It's still unclear whether this could also be the case for booster shots.

What This Means For You

COVID-19 vaccine booster shots are currently under FDA review. Experts recommend checking in with your state’s health department to get the latest information on where and when boosters will become available.

There May Be Some Benefits to Mixing and Matching

Early preliminary research suggests that booster mixing can induce stronger immune responses.

This UK-based study found that mixing doses of the AstraZeneca vaccine with an mRNA vaccine produced a more amplified immune response against the COVID-19 spike protein compared with getting two doses of AstraZeneca.

Another research study, published in Nature Medicine, found similar results. When Pfizer or Moderna vaccines were used as a second dose to AstraZeneca, it led to a stronger immune response when compared with two doses of AstraZeneca, the study found.

Booster research is still ongoing. If the data proves that booster mixing is safe and effective, it could potentially help avoid any vaccine supply shortages and increase the speed of booster rollout.

“The most important thing is to get vaccinated and worry less about which you’re getting vaccinated with,” Swartberg says. “I would say the same thing about boosters if they are advised.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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