The Booster Shot's Been Updated. Experts Explain What It Is and Who Should Get It

The bivalent boosters are recommended by the CDC for people over the age of 12 who have already had their primary vaccination series

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With the winter months and flu season ahead, it may be time to consider getting a COVID bivalent booster shot.

Last month, the U.S. Centers for Disease Control and Prevention signed off on updated versions of the booster shots, and pharmacies and other vaccination sites began administering them around Labor Day weekend. But only a small percentage of the fully vaccinated population has opted to receive them, mostly those in an older age demographic.

During NBC10 Boston's latest "COVID Q&A" discussion, Tufts Medical Center's Dr. Shira Doron, Brigham and Women's Dr. Daniel Kuritzkes and Boston Medical Center's Dr. David Hamer explained what is different about the bivalent booster shots from the original formulation, who should get them and how long you should wait after an infection.

What is the bivalent booster shot?

The bivalent shots target both the original coronavirus strain and the currently circulating omicron subvariants BA.4 and BA.5.

"It's meant to give protection against both the original virus simulated strains but also omicron-related subvariants," Hamer said. "It's complicated, because a lot of the studies look at neutralizing the antibodies and how effective they are at neutralizing the virus in vitro, but I think both of these help strengthen cell-mediated immunity against the virus, which we suspect is important for preventing more severe disease, hospitalization and sort of longer-term protection."

The CDC voted Thursday to recommend updated versions of both the Pfizer and Moderna coronavirus vaccine boosters, paving way for a widespread rollout as early as next week.

Who should get the bivalent booster?

The bivalent boosters are recommended by the CDC for people over the age of 12 who have already had their primary vaccination series -- either two shots of the Pfizer or Moderna vaccines or the single-shot Johnson & Johnson one.

"I think that the uptake has been very poor if you look at that whole group," Doron said. "But if you look at the older age group, it hasn't been as poor. It's been more reassuring."

There was just no reason to keep giving the old vaccine from a strain that is long, long gone.

Approximately 4% of Americans currently eligible to receive the bivalent shots have actually gotten them, according to CDC data. Approximately 16% of all fully vaccinated people have gotten the shot in Massachusetts, state data shows, but 45% of people over the age of 75 have done so.

"There are many experts who feel that that recommendation should have been a little bit more targeted to those who are older and with underlying comorbidities," Doron said. "Perhaps the messaging does need to change and it does need to be sort of more transparent about who's at the highest risk, what we know about what this vaccine will and will not do and what we do know right now is very little, actually."

The experts said there is a lack of data around the bivalent booster, since the shots were distributed without results from human trials — though there was still good reason to develop it. 

"We know that it appears to generate very good neutralizing antibody activity against the omicron variant, better than the original vaccine," Doron said. "We can't talk about efficacy. We can't talk about how many infections it will prevent it. We can't talk about how many hospitalizations it will prevent. We simply can't. But it was time to update the vaccine. There was just no reason to keep giving the old vaccine from a strain that is long, long gone."

The FDA authorized new COVID boosters targeting the Omicron BA.4 and BA.5 subvariants, and Dr. Uché Blackstock says you should expect annual booster shots.

Laboratory studies found that the boosters generated strong antibody responses against BA.4 and BA.5, and human trial data showed that a similar vaccine yielded a strong antibody response against the initial omicron strain, BA.1. But doctors are skeptical that it will prevent infections entirely.

"What is not at all there is to what extent the booster will prevent symptomatic infection. And I actually have pretty low expectations of that," Kuritzkes said. "And I don't think that beyond several weeks after getting boosted, people are going to have any significant protection against symptomatic COVID. I do think that getting boosted is going to protect people from getting severe disease and that, particularly older people and people who have the all the same medical conditions we've been talking about for three years, should get boosted again to sustain high levels of immunity."

How long after COVID can you get a booster?

Hamer said there is at "at least one study that suggests that, if you got it fairly close to that infection and sort of wanted the peak antibody levels, it may make sense to wait at least three months before considering the booster so that you gain more you benefit more from the booster."

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