Which COVID booster shot should you get? – CNET

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As omicron starts to account for the majority of COVID-19 cases in the US, health officials are turning up the volume on their call for COVID-19 vaccine boosters as well as other public health measures, including masks, social distancing and COVID-19 tests prior to gatherings. 

Though information available now does suggest that omicron is causing less severe COVID-19 disease compared with the delta variant, omicron’s extreme contagiousness or transmissibility means it can affect a lot of people at once, posing a threat to our health care system and to the many patients who will need hospital care. Because omicron is also leading to more breakthrough COVID-19 cases in fully vaccinated people (and is causing more COVID-19 reinfections, or people getting sick a second time), public health officials are urging everyone who’s eligible to go and get a booster shot of Pfizer’s or Moderna’s COVID-19 vaccine. (Johnson & Johnson’s vaccine remains available, but concerns over a rare but dangerous side effect led the US Centers for Disease Control and Prevention to recommend an mRNA vaccine or booster dose over a shot of J&J.) 

At a press briefing Wednesday, CDC Director Dr. Rochelle Walensky said that while health officials haven’t yet changed the definition of fully vaccinated, the recommendation is to get a booster as maximum protection against COVID-19. 

“What I can tell you is that you are 10 times more likely to have a case of COVID if you are unvaccinated compared to if you are vaccinated and boosted,” Walensky said. “You are 20 times more likely to die of COVID if you are unvaccinated compared to if you’re vaccinated and boosted.”

Everyone as young as age 16 is eligible for a booster, and extra doses of COVID-19 have been recommended for all adults since November. If you still need yours, here’s what to know about how mixing COVID-19 vaccines works, and which one you should pick. 

What’s the difference among 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

In October, the US Food and Drug Administration authorized heterologous booster doses or a “mix and match” approach to COVID-19 vaccines. This means a person who originally received Moderna’s vaccine can receive Pfizer as a booster, or someone who got Johnson & Johnson’s vaccine can get a booster of Pfizer or Moderna. 

What are the benefits of ‘mixing and matching’ COVID-19 boosters?

Individual choice in boosters means health care providers can make recommendations based on patients’ circumstances, and also allow people to get whatever vaccine is most convenient for them. A member of the CDC’s advisory panel, which meets prior to recommending a vaccine or booster, pointed out at a meeting about mixed boosters that allowing the approach could lead to fewer doses being wasted if, for example, health care providers have to open only one bottle of vaccine for patients in the waiting room. Hopefully, more flexibility with boosters will lead to an easier vaccination process in places that administer many doses at once, such as nursing homes. It also means people who originally received Johnson & Johnson’s vaccine can get Pfizer or Moderna as a booster shot. 

In a study published in the journal Nature in May, 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. 

Research published recently in The Lancet (which tested seven vaccines from around the world as boosters, including the three available in the US) showed that mixing COVID-19 vaccines for boosters is effective, with mRNA vaccines producing the biggest response

Early research funded by the National Institutes of Health prior to the CDC’s recommendation also found that mixing vaccines is safe and effective, or perhaps even beneficial in some cases. 

According to booster data the CDC is collecting on primary series and booster choice, more than 5 million Americans so far have opted for a different vaccine brand as a booster. (Most have chosen their original vaccine as a booster, if they received Moderna’s or Pfizer’s vaccine originally.) Countries outside the US, including Germany, Canada, Sweden, France, Spain and Italy, have been officially allowing people to receive two different vaccines as a primary series (or even recommending they do so). 

Which booster shot should I get if I got Pfizer?

Both mRNA vaccines, Pfizer and Moderna, have proven to be effective and continue to protect against severe disease caused by COVID-19. A study published by the CDC in September that compared vaccine effectiveness among adults in the real world found that two doses of Moderna’s vaccine were 93% effective at preventing hospitalization, two doses of Pfizer were 88% effective and one dose of Johnson & Johnson was 71% effective. 

Pfizer’s booster is the same dose as its original vaccine (30 micrograms), while Moderna’s booster (50 micrograms) is half the size of its original vaccine. Johnson & Johnson’s booster is also the same size as its original vaccine (though it’s recommended all adults choose Pfizer’s or Moderna’s vaccine). In a study that examined people’s responses to all three vaccines as boosters, people who originally got Pfizer had the strongest antibody response to a Moderna booster. However, that study examined a full dose of Moderna (100 micrograms), rather than the authorized half-dose of the company’s booster, which likely minimizes Moderna’s edge over Pfizer, The Atlantic reported. 

Read more: Pfizer COVID booster gets CDC approval for all adults

For most adults who were vaccinated with Pfizer, sticking with another dose of Pfizer makes the most sense, Dr. Robert Wachter, chair of UC San Francisco’s Department of Medicine, told the Los Angeles Times.

“I got Pfizer and stuck with getting another Pfizer — just seemed simpler. Why introduce a new agent into my body for probably zero, or maybe tiny, benefit?” he told the LA Times. “But if your goal were to give yourself any possible advantage in immunity, you can make an argument to switch to Moderna.”

If you’re in a group that would benefit most from every bit of immunity (which includes the elderly and people with health conditions that make them most susceptible to severe COVID-19), it might be worth a quick call to your health care provider to discuss your personal circumstances. However, the urgency of a new variant might also influence your decision, which includes what’s available to you the soonest. 

Teens as young as 16, who are now eligible for Pfizer’s booster after the CDC recommended boosters for 16- and 17-year-olds, will need to stick with Pfizer for a third dose as Moderna and Johnson & Johnson aren’t authorized for anyone under age 18 yet. 


The definition of “fully vaccinated” hasn’t changed. A person is considered fully vaccinated two weeks after their second dose of Pfizer or Moderna, or two weeks after a single dose of Johnson & Johnson. 

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What if I got Moderna? 

Similar to Pfizer, most Moderna recipients probably don’t have a need to choose a different booster, unless how quickly they can get an appointment is an issue.

There might be exceptions — if you had an allergic reaction to Moderna’s vaccine, for example, you should consult a doctor and choose a different vaccine for future shots. An early report on Canadian data also suggested Moderna might carry a higher risk of myocarditis, an uncommon side effect of the mRNA vaccines mostly seen in men under 30, compared to Pfizer. With this assumption, a man under 30 who originally received Moderna but is concerned about myocarditis could ask his doctor about switching to another vaccine. But again, Moderna’s booster is a smaller dose than its original vaccine, which could be a factor in your decision. 

Read more: Moderna COVID booster recommended for all adults. What to know 

Which booster should I get after J&J? 

People who received Johnson & Johnson’s vaccine should get either Moderna or Pfizer as a booster, the CDC says

The recommendation followed a meeting of a committee of doctors and scientists that advises the CDC who discussed rising concerns of a rare but serious blood-clotting disorder associated with Johnson & Johnson’s vaccine, called thrombosis with thrombocytopenia syndrome. Since the CDC paused the distribution of the disorder to investigate, more information revealed that it’s less rare than previously understood and occurs in both men and women. (Although still rare over all, occurring in 57 cases out of 16.9 million doses of Johnson & Johnson given, per the CDC, women ages 30 to 49 are at higher risk of the disorder with about 1 out of 100,000 women experiencing it). Nine people have died from TTS and all cases required hospitalization or ICU admission, according to a CDC presentation

A big reason for the CDC’s preferential recommendation on COVID-19 vaccines is the safety, effectiveness and wide availability of Pfizer’s and Moderna’s vaccines in the US. However, Johnson & Johnson still has emergency use authorization for its COVID-19 vaccine, and a booster dose is available to you if you choose to get it for any reason, including having a prior allergy to an mRNA vaccine. 

In a statement, Johnson & Johnson said the company “remains confident in the overall positive benefit-risk profile of its COVID-19 vaccine.” 

“The safety and well-being of those who use the Johnson & Johnson vaccine continues to be our number one priority,” Dr. Mathai Mammen, the company’s global head of research and development. said in the statement. “We appreciate today’s discussion and look forward to working with the CDC on next steps.”

Read more: What to know if you got Johnson & Johnson’s COVID vaccine

Do I have to get a booster? 

The CDC’s recommendation is that all adults in the US “should” get a booster. This is because even if the omicron variant lowers the efficacy of the vaccines, scientists expect COVID-19 vaccines to remain protective against severe disease.  

Before omicron, earlier in November, the CDC advisory panel voted unanimously to recommend boosters for all adults, but they also acknowledged that some people need them more than others. The guidance was that people age 50 and older “should” get a booster (a younger age than the previous guidance for everyone age 65 and older), in addition to other groups who “should” get one because of a clearer benefit, including adults living in long-term care facilities and everyone who received Johnson & Johnson’s vaccine. For all other adults, the choice was more dependent on personal circumstances or preference. Because of the newer variant which may increase risk of infection in people who already had COVID-19 or those who are fully vaccinated, officials are calling for maximum protection for everyone eligible — age 16 and up. 

Are you fully vaccinated after your booster? 

Importantly, the definition of fully vaccinated hasn’t changed (though it might in the future). You’re still fully vaccinated two weeks after your second Pfizer or Moderna shot or two weeks after your Johnson & Johnson vaccine. Whether someone has received a booster doesn’t affect their “fully vaccinated” status. 

Can I mix and match the first two shots?

No, the CDC’s statement on mixing COVID-19 vaccines only applies to boosters. 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 in greater numbers, 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 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.