Members of anvoted unanimously on Friday to recommend boosters for everyone who received Johnson & Johnson’s one-dose COVID-19 vaccine. Later in the meeting, members addressed the question of whether people need to stick to their original vaccine for boosters, especially in light of preliminary data that suggests mixing COVID-19 vaccines, or “heterologous priming,” is effective or even beneficial in some cases. There wasn’t a vote, and no authorization is on the table quite yet, but the question is growing increasingly loud: Do you need the same vaccine for a second (or third) coronavirus shot?
Some adults who initially received Pfizer are now eligible for a booster shot of Pfizer, including adults who are at risk of severe COVID-19 because of a health condition and folks whose jobs put them at high risk of transmission. (Immunocompromised people who received an mRNA vaccine have been eligible for a third dose of Moderna or Pfizer for a while.) Moderna’s and Johnson & Johnson’s booster doses have recently received recommendations for authorization by the FDA’s advisory committee, but are waiting on official authorization by the FDA and recommendations for use and distribution by the US Centers for Disease Control and Prevention.
But before anyone is given the stamp of approval to mix vaccines, the FDA will likely have to change the language in its emergency use authorization for the coronavirus vaccines to allow different combinations, The New York Times reported.
Mixing COVID-19 vaccines is being done in other countries, and it’s also being done unofficially in medical offices as some people seek out COVID-19 boosters for themselves. But before they make an official recommendation or give any sort of green light, scientists in the US need to determine whether the benefits of mixing different vaccine types outweigh the potential risks, and consider the differences between the vaccines.
For starters, while all three vaccines have the same effect (though they vary slightly in their efficacy), the way they function is a little different. Pfizer and Moderna are mRNA vaccines, which teach our cells to make a specific protein and build immunity against a virus. Johnson & Johnson is a viral vector vaccine, which uses a harmless virus to activate an immune response and tell our bodies what to fight in future infections. Both vaccine types prepare our immune systems for COVID-19 infection, and.
Whether you’re eligible for a booster now, want to be prepared for a potential third shot in the future or are making plans to get your first COVID-19 shot, here’s what we know now about mixing different vaccine brands.
I qualify for an extra shot right now. Do I have to get the same one?
The newest CDC recommendation for some adults who received Pfizer only applies to those who got Pfizer for their initial coronavirus vaccine series. So if you qualify, you’ll get another shot of Pfizer at least six months after your second dose.
If you’re “moderately or severely immunocompromised,” according to the CDC, and received Pfizer or Moderna as your COVID-19 vaccine, it’s recommended that you receive another dose at least four weeks after your second shot. If you got Pfizer for your initial vaccine shot, you should get a third dose of Pfizer, and the same goes for Moderna. However, the CDC says that if you don’t know what brand you received or if that brand isn’t available to you, you could get the other mRNA vaccine. (aren’t included in this recommendation by the CDC.)
So right now, the only CDC-endorsed “mix and match” approach is for immunocompromised people who received Moderna or Pfizer and can’t receive the same mRNA vaccine for whatever reason (you lost your vaccine card and can’t remember, the first one isn’t available in your area, etc.) But this flexibility could carry over to booster recipients in the future, including during mass vaccination efforts in places like nursing homes where providers will only need to carry one type of mRNA vaccine for all residents, an advisory committee member noted Friday, or when people who can’t receive their original vaccine for whatever reason.
What if I got a different shot by accident?
Generally, the CDC says that because data on people who’ve received two different vaccines (called a “mixed series”) is limited, it’s preferable to get your second dose of the same vaccine, even if it means waiting longer than the recommended time. But if there was a mix-up at the clinic or you accidentally received Pfizer for the second dose when your first shot was Moderna, you don’t need a third dose of either vaccine and you’re still considered fully vaccinated two weeks after your second dose of an mRNA vaccine, according to the CDC.
If you got Pfizer or Moderna for the first shot, then Johnson & Johnson for the second dose because you have a contraindication (an allergic reaction to your first dose or another medical reason you shouldn’t get another dose of your first shot), you’re considered fully vaccinated two weeks after your Johnson & Johnson shot, per the CDC.
Is it safe to mix and match?
The fact that the current guidance allows people currently eligible for an extra COVID-19 shot to get a dose of Pfizer if Moderna isn’t available, and vice versa, is likely because scientists determined that the benefits of a third dose of coronavirus vaccine (protection against severe disease) for some people outweigh the unknown risks that may come from receiving another kind of shot.
But before scientists and public health officials can go on record recommending a mixed-series vaccine for the general population, they need to determine that it’s a safe practice.
“There are theoretical advantages to receiving different vaccine types, in that different parts of the immune system can be impacted for protection,” says Dr. Margaret Day, physician and vaccine co-chair at University of Missouri Health Care. “But medical research is ongoing about antibody responses and T cell responses as well as safety and efficacy in trials.”
At the latest FDA advisory committee meeting, some members pointed out that while official data on mixing COVID-19 vaccines is still sparse, it’s being done, and there’s a need for scientists to give the public some guidance. Preliminary data from the US also suggests that mixing a viral vector vaccine (Johnson & Johnson) with an mRNA vaccine produces a stronger antibody response than receiving a second dose of Johnson & Johnson, with Moderna as a booster especially.
Information from outside the US is also promising, and other countries have been officially allowing people to receive two different vaccines, including Germany, Canada, Sweden, France, Spain and Italy, per The New York Times. (In some cases, mixing vaccine types comes down to what’s available.) In a study published in the journal Nature, researchers in Spain found that people who received one dose of AstraZeneca (a similar vaccine to Johnson & Johnson) and then received a dose of Pfizer seem to produce a higher antibody response than people who receive two doses of AstraZeneca. It isn’t clear whether this group had a higher immune response than people who received two doses of Pfizer.
When or if public health officials determine that a mixed vaccine regimen is safe and effective, it may prompt US public health officials to make certain vaccine recommendations for specific groups. In the United Kingdom, for example, the National Health Service says that for people under age 40 who don’t have a health condition, it’s “preferable for you to have the Pfizer/BioNTech or Moderna vaccine instead of Oxford/AstraZeneca,” because of AstraZeneca’s link to a very rare but serious blood-clotting disorder in younger people. Germany issued a similar recommendation about mixing AstraZeneca with an mRNA vaccine.
Johnson & Johnson’s shot in the US has also been linked to the same rare-but-serious blood-clotting disorder, and the CDC says, “Women younger than 50 years old especially should be aware of the rare but increased risk of this adverse event, and they should know about other available COVID-19 vaccine options for which this risk has not been seen.” If a mixed series is authorized, people in the US who originally received Johnson & Johnson but are at higher risk for a rare side effect would be able to opt for a different booster.
But isn’t mixing vaccines already being done in the US?
In San Francisco, some Johnson & Johnson recipients have gone ahead and received an mRNA shot after the city made an “accommodation” for those asking for one, though it hasn’t changed health policy in San Francisco.
The vaccine for Ebola, made by Johnson & Johnson, uses a mixed-dose approach. According to the EU Research and Innovation Magazine, the two-part vaccine is made up of two slightly different technologies and was developed this way because of the immune response it could produce.
Day says that while sometimes different vaccine brands are used, “a major difference is having years’ worth of data available for review for those.”
While research for everything else is underway, Day says the best thing you can do is to complete a COVID-19 vaccine series as currently reviewed.
“Ultimately, the absolutely most important action people can take today to protect themselves and their communities against COVID-19 is getting their initial COVID-19 vaccine series,” Day says. “We will be faced with questions about the best strategies for initial series vaccination and additional vaccinations and booster doses, and those answers will become available in time.”
In the US, 68.5% of adults are fully vaccinated, according to CDC data. According to Our World in Data, 48% of the world’s population has received at least one dose of a coronavirus vaccine. Only 2.7% of people in lower-income countries have received a COVID-19 vaccine.
The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.