What to Know About Pfizer's and Moderna's Bivalent COVID Boosters

Jessica Rendall Wellness Reporter
Jessica is a writer on the Wellness team with a focus on health technology, eye care, nutrition and finding new approaches to chronic health problems. When she's not reporting on health facts, she makes things up in screenplays and short fiction.
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Jessica Rendall
8 min read
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What's happening

Updated COVID boosters from Pfizer and Moderna are available to everyone 6 months and older. Some adults can get Novavax for a booster instead.

Why it matters

As the virus mutates, boosters have become necessary to restore protection given by the original vaccines or past infections.

What's next

Viruses like COVID-19 spread really well indoors. OIder adults in their 60s and up, as well as younger folks with medical conditions, remain the most vulnerable to severe disease or death and will especially benefit from a booster dose.

Out of a priority for "transparency and vaccine safety," the US Centers for Disease Control and Prevention and US Food and Drug Administration said in a joint statement Friday that one of the many systems meant to monitor vaccine safety detected a potential signal for Pfizer's new COVID-19 booster and stroke risk in adults age 65 and up. Older adults have the highest risk of hospitalization and death from COVID-19, which are prevented by boosters and vaccines. 

Though it merits investigation, the CDC said it's "very unlikely" there's a true clinical risk, as the many other monitoring systems -- including the Vaccine Adverse Event Reporting System, or VAERS; a preliminary study from the Veterans Affairs database; and Pfizer-BioNTech's global vaccine safety database -- haven't found any increased risk of ischemic stroke within 21 days of vaccination compared with 22 to 42 days post-vaccination.

"All signals require further investigation and confirmation from formal epidemiologic studies," health officials said. "When one system detects a signal, the other safety monitoring systems are checked to validate whether the signal represents an actual concern with the vaccine or if it can be determined to be of no clinical relevance." Moderna's bivalent vaccine didn't spark the same preliminary signal, health officials said, and no changes in vaccine recommendations have been made for any age group.

In a statement, Pfizer and BioNTech pointed to the fact that neither the companies nor the FDA or CDC have found any potential safety signal outside of the VSD system, and that to date, the companies have actually observed a "lower number of reported ischemic strokes" following a boost with Pfizer's bivalent vaccine when compared with the general incidence rates in the older population.

"With hundreds of millions of doses of the original and Omicron BA.4/BA.5-adapted bivalent Pfizer-BioNTech COVID-19 vaccine administered globally, the benefit-risk profile of our vaccines remains positive for all authorized indications and age groups," the companies said. 

Health officials are having a public meeting on Jan. 26, which anyone can watch online, to discuss COVID-19 vaccines and boosters, and will go over data from the CDC's and FDA's investigation into the possible but unlikely link between Pfizer's booster and stroke for older adults. 

Anyone can have a stroke, but the risk of having one doubles for each decade of life after age 55, according to Johns Hopkins Medicine. Adults over age 65 -- the only group centered in the investigation announcement from health officials -- have also been at highest risk of severe COVID-19, and have accounted for more than 81% of all deaths from COVID-19. 

Boosters have been especially beneficial to the older population at preventing severe disease and death. A report published Oct. 7 by the US Department of Health and Human Services found that COVID-19 vaccines were linked to about 650,000 fewer hospitalizations and 300,000 fewer deaths in seniors and other people who were enrolled in Medicare in 2021. 

Updated boosters are available to everyone age 6 months and older in the US. Here's what we know about them. 

Vaccine needles arranged on a black table.
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What we know about the bivalent vaccines and how well they work 

The bivalent formulas made by Moderna and Pfizer-BioNTech target both the "original" version of COVID-19, as well as the BA.4 and BA.5 subvariants of omicron. Both are available for adults and children as young as 6 months.

Though BA.4 and BA.5 are no longer the subvariants causing disease in the US (XBB.1.5 is poised to take over BQ.1 and BQ.1.1), some lab studies suggest that the bivalent boosters will be sufficient at neutralizing XBB.1.5 and preventing severe disease. And real-world information is backing up the effectiveness of the new boosters compared with the original COVID-19 vaccine formulas.

New, real-world data from Israel confirms that the new COVID-19 vaccines formulated to work against the omicron variant are effective at keeping people out of the hospital, according to findings posted by The Lancet. The study, which hasn't yet been peer-reviewed, included information from more than 600,000 people age 65 and older. 

This real-world data backs up earlier information from the CDC, which found that in November 2022, monthly hospitalization rates for adults who were vaccinated but didn't get an updated booster were 2.7 times higher compared with adults who did get a new booster. The rate of hospitalization in unvaccinated adults was 16 times higher compared with adults who got a new booster.  

Though there's positive data available now, a lack of of real-world data at the beginning of the bivalent booster campaign gave some researchers pause. When they were authorized by the FDA, the agency made its decision based on clinical trials of a slightly different bivalent booster, which targets the BA.1 version of omicron instead of BA.4/BA.5. In addition, there were mice studies on the BA.4/BA.5 formula. This approach was previously unprecedented in the COVID-19 vaccine campaign, but health officials say it isn't too far off the way we approve influenza vaccines. Every year, the flu vaccine is tweaked with a strain believed to be the best target. And the new COVID-19 boosters also don't introduce any new vaccine ingredients.

"Bivalent and multivalent vaccines are very common and modifying a vaccine to include different virus strains often does not require a change in other ingredients," FDA Commissioner Dr. Robert M. Califf said in August in a tweet. "FDA has extensive experience with reviewing strain changes in vaccines, as is done with the annual flu vaccine."

Who can get Novavax's booster? 

Adults who've been vaccinated against COVID-19 -- but haven't yet received any booster -- can get a dose of Novavax as their booster. It doesn't matter which vaccine you originally received -- Pfizer, Moderna, Johnson & Johnson or Novavax. 

Read more about the Novavax vaccine here

When should I get the updated booster? 

The updated mRNA boosters (from Pfizer and Moderna) are authorized by the FDA for adults who've gone at least two months since their last vaccine dose, whether it was a booster shot or a primary series. It doesn't matter which vaccine you originally received, and it shouldn't matter which brand you choose now. Moderna's new booster, like its previous vaccine, is a slightly larger dose (50 micrograms) than Pfizer's (30 micrograms). 

For babies, toddlers and preschoolers who are eligible for smaller doses of the updated formulas, it's a little different. Children 6 months through 5 years who got Moderna's primary series vaccine can only get an updated dose of Moderna at least two months after their second shot. Children 6 months through 4 years who started Pfizer's primary series can get the bivalent vaccine as their third dose, instead of the "original" third dose. Children in this age group who already got three doses of Pfizer aren't eligible for an updated booster right now.

If you're 18 or older and were vaccinated earlier in the pandemic but haven't gotten any booster yet, you can get a Novavax shot at least six months after finishing your primary series if you prefer it over an mRNA vaccine.

If you're in your 60s or older -- or even if you're in your 50s -- the advice among medical experts is clear: Get the updated booster as soon as you can. Older adults are more vulnerable to severe illness and death from COVID-19. If you're younger and have a medical condition that makes you more vulnerable to severe disease, including diabetes, heart disease and more, you could also especially benefit from the boost in protection against severe illness.

Health officials have encouraged everyone to get their updated boosters, and Moderna and Pfizer-BioNTech have authorized formulas for children as young as 5. However, on an individual level, timing advice for people who very recently had COVID-19 (we're talking within the last few months, not last year) isn't quite as cut-and-dry as it is for higher-risk adults, or people who are several months out from their last bout of COVID-19. 

At a panel meeting of the CDC's scientific advisers, a committee that meets before the CDC recommends a vaccine, a few members expressed concern that some people would be better off waiting longer than two months between their last shot and this new booster, especially people who have recently had COVID-19 and still have relatively high immunity. (In its general vaccine guidance, the CDC says that people can wait three months before getting the shot if they're getting over COVID-19.) 

And while myocarditis is rare overall, younger men and teenage boys appear to be at higher risk post-vaccination and waiting longer between vaccine doses appears to reduce this risk. 

From an immune response perspective, some infectious disease doctors have suggested waiting as long as four to six months between your last COVID-19 infection or vaccine to get the most bang out of the new booster. Fauci told PBS that if you tested positive for COVID-19 recently, "you should wait about three months, at least three months from the time that you had a prior infection" before getting the new booster. Fauci added that because he had COVID-19 in the middle and end of June, he was waiting until the end of September to get boosted.

Fauci ended up getting his booster live on The Late Show With Stephen Colbert in early October.

But individual immunity is only one piece of the puzzle, when we're talking about a respiratory virus as contagious as COVID-19. People who may only have very mild symptoms they dismiss as a cold or allergies can still pass along an infection to their more-vulnerable family or friends.

"Even if you yourself are on the low-risk side, you're going to have family and friends you're going to see," Dr. Ashish Jha, the White House COVID-19 Response Team Coordinator said on Andy Slavitt's podcast in October, as reported by CNBC

"You don't want to be the person who gives it to your grandma." 

Dr. Jayne Morgan, executive director of the COVID Task Force at Piedmont Healthcare, said that it's important to get a booster right now so we can "stem the tide" on the pandemic.

"You want to have this booster while omicron is circulating. The whole point of bringing the booster out now is so that we can stop chasing this variant," Morgan said, adding that it's unclear what variants or subvariants will be in our future, and if (or how much) they'll evade our protection from vaccines, infections and treatments. 

The vaccines and boosters have proven to be especially effective at preventing severe disease in older adults. A report published Oct. 7 by the US Department of Health and Human Services found that COVID-19 vaccines were linked to about 650,000 fewer hospitalizations and 300,000 fewer deaths in seniors and other people who are enrolled in Medicare in 2021. More than 81% of COVID-19 deaths occur in people over age 65, according to the CDC. 

Where can I get the new booster? 

You should be able to use the vaccine finder site Vaccines.gov to find an updated vaccine near you. When you're choosing your updated booster from either Pfizer-BioNTech or Moderna, make sure to select the shot that says "Newly Authorized Bivalent" in bold text. Primary series vaccines, or the first two doses, are still available for people who haven't received any vaccine yet.

Smaller doses of the original vaccines are also still available for kids as young as 6 months. For those who are getting the Novavax booster, you'll find it under "Primary vaccines." 

Can I get a flu vaccine at the same time as my booster? 

Yes, according to the CDC. There's no recommended waiting period between the seasonal flu shot and the COVID-19 vaccines.  

So far, the current flu season has been the most severe since the 2010-2011 flu season. 

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.