Public Health

Second bivalent booster: Who should get another COVID shot and when with Sandra Fryhofer, MD


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Do you need a second COVID bivalent booster? Get the latest on new COVID vaccine booster recommendations from the CDC and the recent changes to simplify COVID-19 vaccine guidelines from Sandra Fryhofer, MD, AMA’s liaison to the Advisory Committee on Immunization Practices (ACIP) and a member of ACIP’s COVID-19 Vaccine Workgroup. AMA Chief Experience Officer Todd Unger hosts.


  • Sandra Fryhofer, MD, chair, AMA Board of Trustees; AMA’s liaison, Advisory Committee on Immunization Practices (ACIP); member, ACIP’s COVID-19 Vaccine Workgroup

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Unger: Hello and welcome to the AMA Update video and podcast. Today, we're talking about the new COVID vaccine booster recommendations from the CDC. A spring booster dose of the updated bivalent COVID vaccine is now an option for some. But who should get it and when?

Here to answer those questions is Dr. Sandra Fryhofer, the AMA board chair and AMA's liaison to ACIP, the CDC's Advisory Committee on Immunization Practices. Dr. Fryhofer is also a member of the ACIP's COVID vaccine work group. I'm Todd Unger, AMA's chief experience officer in Chicago. Welcome back, Dr. Fryhofer.

Dr. Fryhofer: Thanks for having me, Todd.

Unger: So, Dr. Fryhofer, what do we need to know about these new booster recommendations from the CDC?

Dr. Fryhofer: Well, older adults and adults with immunocompromising conditions now have the option of getting more COVID protection from an additional dose of the updated bivalent vaccine. FDA has authorized and CDC now recommends an additional bivalent booster dose for those 65 and older and for those with immunocompromising conditions.

As for timing, older adults, those 65 and older, can receive it at least four months after their last dose. People with immunocompromising conditions can get their additional boost a little bit sooner, at least two months after their last dose. And for them, more additional doses may be administered based on their clinical circumstances and at intervals determined by their physician. These options add flexibility for this group of people at higher risk of severe COVID complications.

For young children with immunocompromising conditions, those age six months through four, eligibility for additional booster doses is more complicated and depends on the type and number of vaccines previously received. And although the overarching theme of these new recommendations is flexibility and simplification, dosing for young children remains a little complicated.

However, CDC is in the process of putting together some detailed and specific step-by-step flowcharts to help clinicians determine what dose and what formulation children need and when.

Unger: Dr. Fryhofer, you mentioned the word simplicity. How have the new recommendations been simplified?

Dr. Fryhofer: Well, this is really good news. For those age six years old and older, COVID vaccination recommendations have been greatly simplified. The same mRNA vaccine formulation will be used for all vaccine doses for everyone.

The original monovalent vaccines are no longer recommended. And at least for now, the bivalent vaccine formulation, which is half original and half Omicron BA.4/BA.5, will be used for all vaccine doses for everyone.

Unger: Well, Dr. Fryhofer, tell us more about the timeline of this recommendation and why the FDA and the CDC are offering an additional booster to those selected groups right now.

Dr. Fryhofer: Well, it all happened last week. On Tuesday, April 18, FDA gave the thumbs up for a second updated booster for those 65 and older and for those with immunocompromising conditions and using the bivalent vaccine for all vaccine doses. Then on Wednesday, April 19, ACIP, which is CDC's Advisory Committee on Immunization Practices, met and discussed FDA's amended authorizations and also reviewed updates for vaccine safety and vaccine efficacy.

There was no formal ACIP vote. The CDC director, Dr. Rochelle Walensky, was the decider. And she sealed the deal with her signature later that evening.

Additional bivalent boosters are now an option for these specific groups. Monovalent vaccines are no longer recommended. The bivalent booster first became available in September 2022 around Labor Day. And we know that the efficacy of mRNA vaccines wanes with time.

An additional vaccine dose restores immunity. Some people are now at least six months out from their last bivalent vaccine dose. But many people have not had even one bivalent COVID vaccine dose.

Unger: Well, how about those people? Does this affect vaccine recommendations for those who still have not even been vaccinated?

Dr. Fryhofer: Yes. And that is a great question. Again, simplification, the new recommendation says most unvaccinated individuals aged six years old and older only need a single dose of the updated vaccine, which is a bivalent vaccine, rather than multiple doses of the original monovalent mRNA vaccines.

The regimen for younger children is not quite as simple. Children aged six months through four years old need two to three bivalent mRNA doses. Five-year-olds need one or two bivalent doses. For these younger children, the number of doses is product dependent.

So the regimen for children is still complicated. And this was brought up in the discussion by several ACIP members. CDC is putting together detailed flow sheets to help clear up any confusion, however.

Unger: So those changes, what led to them?

Dr. Fryhofer: Well, COVID has gone from pandemic to endemic. People who've been vaccinated have vaccine-induced immunity. People who've had COVID develop infection-induced immunity. People who've been both vaccinated and previously infected with COVID have hybrid immunity.

There's still a small subset of people who've neither been vaccinated nor infected. But that group's getting smaller and smaller. The fact is most everyone in the U.S. aged five and older already has COVID antibodies, either from vaccination or from previous infection or both.

And FDA said that for those with prior infection, their immune response after one dose of vaccine was comparable to the immune response after two vaccine doses. However, younger children, those age six months through five years old who have not been previously vaccinated, do need more than one vaccine dose. They need a prime-boost, which means two or three mRNA vaccine doses depending on the vaccine product use, including at least one bivalent vaccine dose.

Unger: So, Dr. Fryhofer, you mentioned hybrid immunity and the fact that if you've had a COVID infection before. Does that affect the recommended time interval for getting a boost if you had a recent COVID infection?

Dr. Fryhofer: Well, a lot of people have COVID don't even know they've had it. But CDC is already on record saying to wait at least three months after a known COVID infection to get a COVID vaccine dose. So that's a great question, Todd.

Unger: So this new recommendation, it only applies to people who are 65 and older and for those with immunocompromising conditions. What about people that are under 65? When should folks that are younger than that plan on getting a vaccine boost?

Dr. Fryhofer: FDA says it intends to address additional boosters for those younger than 65 when their advisory committee VRBPAC meets in June. And at that time, FDA will also address any needed changes and the strains included in the vaccine. Changing the strains for a vaccine that's already been studied isn't new. We do this for flu vaccine every year.

WHO's Technical Advisory Group on COVID-19 Vaccine Composition, which is also referred to as TAG-CO-VAC, they're meeting in May to discuss COVID vaccine antigen composition. And I'm sure FDA will take those recommendations into consideration when they meet in June. And this should give vaccine manufacturers time to make any recipe changes. So updated vaccines can be ready to go by fall if needed.

Unger: And one of those recipe changes, so to speak, was the move from the monovalent to the bivalent. Just for those out there that need a little bit of a refresher on that, can you review the difference between those two?

Dr. Fryhofer: Sure. Bivalent means it's half original strain and half Omicron BA.4/BA.5. Now remember, mRNA COVID vaccines trigger antibodies to spike protein. And although BA.4 and BA.5 are different subvariants and have different mutations, their spike protein just happens to be the same. So that's why this new bivalent vaccine targets both.

You may recall Omicron BA.1 bivalent studies found adding a second COVID virus to the original vaccine broadens the antibody response and results in higher antibody titers for Omicron variants and higher antibody titers against other COVID variants as well. And the resulting antibody titers were as high or higher than for vaccines containing only the original vaccine strain.

Unger: Dr. Fryhofer, are we out front on this in the U.S.? Are other countries already doing this?

Dr. Fryhofer: No, we are not the first ones to do this. Both Canada and the United Kingdom are already offering second-bivalent booster doses to older patients. But their definition of who's considered older is older.

The CDC recommendation starts at age 65. In the United Kingdom, the extra boost recommendation starts at age 75. In Canada, older starts at age 80.

Canada's recommendation, like ours, is permissive and flexible. Canada says these older patients may get it. The U.K. recommendation is more definitive. The U.K.'s equivalent of the CDC says those age 75 and older should get the additional vaccine boost.

Unger: Thinking back to the trajectory of a lot of the vaccines that we've discussed, how does this new recommendation affect the single-dose Janssen vaccine and the protein-based Novavax vaccine?

Dr. Fryhofer: This new recommendation only applies to the mRNA vaccines. And there's no change at least for now in authorization for Janssen's viral vector vaccine or for Novavax's protein-based COVID vaccine. And please note that the available doses of Janssen will expire by the end of May 2023.

Unger: Well, taking a little bit of a step back, how often is COVID still leading to serious illness? And how are we doing on getting people vaccinated?

Dr. Fryhofer: In the United States, COVID still kills about 1,300 people each week. There's still over 100,000 new COVID cases and more than 1,600 hospitalizations for COVID each week. Older adults have higher rates of hospitalization than younger adults.

Unger: So still some high numbers out there. Any updates on which variants are currently circulating?

Dr. Fryhofer: Well, Omicron subvariants are still dominant. XBB.1.5 accounts for more than 78% of circulating strains. Omicron BA.4 and BA.5 are history at this point. XBB.1.16 is now on the rise. And it accounts for 7.2% of new infections nationwide. But what variant is on the menu next?

Unger: That is the question, I guess. On that note, any final thoughts to share? There are a lot of new developments this week.

Dr. Fryhofer: COVID continues to be a very real risk for many people, which is why FDA and CDC encourages everyone to stay current on vaccination. Adults and children age six and older are now considered up to date if they've received a single dose of the bivalent COVID vaccine. But, overall, only 16.7% of the U.S. population has received a dose of the updated booster. And only about 43% of those 65 and older have received the bivalent booster.

COVID vaccines protect from severe disease. COVID vaccines can keep you out of the hospital and save your life. And I hope that this transition to a single formulation, a simpler schedule, a single dose for most and more flexible dosing for people at higher risk will encourage more people to get vaccinated and stay protected.

Unger: I hope so too. Thank you so much, Dr. Fryhofer, for being with us today and providing these important updates on the booster. That's it for today's update. We'll be back soon with another episode. You can find all our videos and podcasts at Thanks for joining us today. Please take care.

Disclaimer: The viewpoints expressed in this video are those of the participants and/or do not necessarily reflect the views and policies of the AMA.