There are three available COVID-19 vaccines in the US. Moderna and Johnson & Johnson have emergency use authorization from the Food and Drug Administration, while Pfizer has full FDA approval. While the question of when and if we'll all need boosters continues to hang, you might be wondering -- can I get a different brand the next time I need a coronavirus vaccine shot?
Mixing COVID-19 vaccines is being done in other countries, and it's been done in the US with other vaccines. But before they make an official recommendation or give any sort of green light, health officials in the US need to determine whether the benefits of mixing different vaccine types outweigh the potential risks if any, as well as consider the differences between the vaccines.
For starters, while all three vaccines have the same effect (though 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 none of the coronavirus vaccines infect us with the actual coronavirus.
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 vaccine dose right now. Do I have to get the same one?
If you're "moderately or severely immunocompromised," according to the Centers for Disease Control and Prevention, 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. Examples of people who qualify right now include organ transplant patients, people who're being treated for tumors or cancer in the blood, people who've received a stem cell transplant, folks with untreated or advanced HIV infection and people with other conditions or who're taking medications that suppress their immune system. If you're unsure whether you need one, talk with your doctor.
If you got Pfizer for your initial vaccine, 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. (Johnson & Johnson recipients who're immunocompromised aren't included in this recommendation by the CDC.)
On Friday, an advisory committee to the FDA found that individuals ages 65 or older and people at high risk of COVID-19 would also benefit from a third shot of Pfizer. This is a different decision from the CDC's recommendation for immunocompromised people, and it hasn't been officially accepted by the FDA or endorsed by the CDC yet. Right now it would only apply to a select group of people who were initially vaccinated with Pfizer.
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, delaying getting your second dose because you're waiting for the right vaccine is preferable to getting a different vaccine at 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 and that the benefits of it outweigh potential risks.
"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."
Information from outside the US shows promising efficacy, though, and other countries have been 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.)
In the US, the National Institutes of Health and the National Institute of Allergies and Infectious Diseases announced a study in June that's testing mixing different COVID-19 vaccines. People in the study who received either Johnson & Johnson, Moderna or Pfizer will receive an extra dose of Moderna.
When or if public health officials determine a mixed vaccine regimen or "heterologous priming" is safe and effective, that may open doors of access for people if they become eligible for booster shots or additional doses. It may also prompt public health officials to make certain vaccine recommendations for specific groups. In the United Kingdom, for example, the National Institute of Health 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 rare but serious blood-clotting disorder in younger people (who have a lower risk of dying from COVID-19 without the influence of another health condition). 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." Should a booster or additional dose ever be needed for this group, and available data shows that a mixed series is safe, it might be safe to assume that the CDC could make a recommendation that people in this group get a different vaccine the second time around.
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 just complete the 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."
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.
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