CDC says people can ‘mix and match’ COVID boosters: What to know

When the CDC recommended boosters Thursday for some people who received Moderna’s COVID-19 vaccine and everyone who received Johnson & Johnson’s, the agency also gave the OK for eligible adults to get a heterologous booster dose if they prefer — a different vaccine from the first brand they received — which some are calling the “mix and match” approach.

Currently, people who received Moderna’s or Pfizer’s booster and are age 65 or older, living in a long-term care facility or age 50 or older with an underlying medical condition “should” get a booster, per the CDC, at least six months after their second dose. Moderna or Pfizer recipients who are at risk of COVID-19 because of an institution they’re involved with (which includes people such as incarcerated adults) or at risk because of their occupation “may” get one if they’re at least 18 years old. Everyone who got Johnson & Johnson should get a booster of COVID-19 vaccine, the agency says. 

The “may” versus “should” language the CDC uses represents who’s most likely to get a clear benefit from a booster. The three vaccines remain effective against severe disease and death caused by COVID-19. Unvaccinated people are over 10 times more likely to be hospitalized with severe COVID-19 or die from the disease than fully vaccinated people. 

Allowing “mix and match” means everyone who’s eligible for a booster can either stick to their original brand or opt for a new COVID-19 vaccine if they prefer. At a meeting Thursday by an independent committee that guides the CDC’s official recommendation, some members expressed a need for clear guidance on who may benefit from getting a different vaccine as a booster and who should stick to their original brand. The CDC should have more guidance and details early next week, the Washington Post reports. 

The booster mix-and-match approach to vaccinating against the coronavirus has been advocated for by some scientists and public health experts, and it’s already being done in countries outside of the US. (Some European countries have allowed or even recommended people receive one dose of AstraZeneca and another of an mRNA vaccine). Although it’s a new concept here in the US, data from a mix-and-match booster trial suggest it’s safe and effective. In particular, people who received Johnson & Johnson have a higher antibody response with an mRNA boost than with another dose of J&J.

As mixing COVID-19 shots becomes a reality in the US, here’s what we know about a mixed vaccine series, and what it could mean if you opt for a different shot. 

What’s the difference between the COVID-19 vaccines? 

While all three vaccines have the same effect — protection against severe COVID-19 disease — 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 infects us with the actual coronavirus. 

What are the benefits of mixing vaccines for a booster?

Individual choice in boosters means health care providers can make recommendations for patients based on their particular circumstances. A member of the CDC’s committee also pointed out at the meeting that allowing mixed boosters could lead to fewer vaccine doses being wasted, if health care providers only have to open one bottle of vaccine for patients in the waiting room, for example. It could also lead to an easier vaccination process in places that administer many doses at once, such as nursing homes. 

People may also opt for a different vaccine if they’re at higher risk for a rare vaccine side effect. Some CDC committee members expressed concern over recommending a second dose of Johnson & Johnson in women ages 18-49 because of the vaccine’s link to a rare but very serious blood clotting disorder in this group, who are people who generally have low risk of severe COVID-19. There is also a link to Johnson & Johnson’s vaccine and rare instances of a neurological disorder, mostly seen in older men. 

CDC advisory committee member Dr. Pablo Sanchez said he wouldn’t have recommended a second dose of Johnson & Johnson if that had been the only option for people who originally received it. And while he agrees Johnson & Johnson recipients should get a booster, “I would prefer that those individuals get an mRNA vaccine,” he said.

Inflammation of the heart, usually resolving quickly, is a side effect that’s been reported after vaccination with an mRNA vaccine, mostly affecting younger men under age 30 after the second dose. A presentation given at the CDC committee meeting suggested that risk of myocarditis might be higher following Moderna’s vaccine compared with Pfizer’s. However, given that Moderna’s booster is a smaller dose than its vaccine, and Pfizer’s booster is the same dose, it’s hard to know whether this will lead to a particular recommendation for boosters.

The bottom line? Mixing vaccines for a COVID-19 booster may be a great benefit to some people, but it ultimately depends on personal circumstances. The CDC is expected to give a little more guidance on which vaccines people should choose, including if it’s best for them to stick to their original brand, within the next week.

Is it safe to mix and match COVID-19 shots? 

A study on mixing with different boosters for all three COVID-19 vaccines found no safety concerns and that the mixed boosters elicited a strong antibody response. 

There isn’t a lot of data on mixing COVID-19 vaccines in the US, because it hasn’t been allowed until now and the only people who’ve done it have gone against the recommendation of the FDA or CDC, and they’ve gotten boosters privately in medical offices or by lying about their vaccination status at vaccine sites.

Information from outside the US is also promising, though, as other countries have been officially allowing or recommending people receive two different vaccines, including Germany, Canada, Sweden, France, Spain and Italy.

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. 

Can I mix and match the first two shots?

No, the CDC’s statement on mixing COVID-19 vaccines only applies to people eligible for a booster dose. As of now, the FDA has only authorized a mixed-series booster, meaning the first coronavirus vaccine series must be one dose of Johnson & Johnson, or two doses of Moderna or Pfizer. 

Once the mixed-series boosters start rolling out to Americans, there will be more data on the safety and effectiveness of a mixed COVID-19 series. Although it might be too early to hope, this might mean that data on mixing for boosters will inform decisions on primary coronavirus vaccine series being used together, making it easier to reach underserved communities, and possibly reducing health care and vaccine inequity. 

The booster rollout has been a controversial one. Officials with the World Health Organization have called on countries such as the US to slow the process of giving booster doses to people who are already vaccinated while much of the world remains unvaccinated against COVID-19. As few as 3% of people in low-income countries have had a coronavirus vaccine, according to Our World in Data.

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.