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Should ‘fully vaccinated’ now include a booster dose? Here’s what the experts say

A booster shot of Pfizer's COVID-19 vaccine is pictured in Longmeadow.
A booster shot of Pfizer's COVID-19 vaccine is pictured in Longmeadow.Lane Turner/Globe Staff

The Centers for Disease Control on Friday expanded COVID-19 booster eligibility to include all adults, clearing the way for millions more Americans to shore up protection against the virus.

Friday’s decision, coupled with data showing that immunity due to the vaccines wanes over time, has raised questions about whether the expansion could pave the way for boosters to become part of the standard COVID-19 vaccination regimen.

Multiple experts said they think the COVID-19 vaccination program will eventually include three doses of an mRNA vaccine or two Johnson & Johnson doses — just not right away. They also emphasized that a more pressing matter is changing the course of the pandemic: Vaccinating those who remain unvaccinated, not deepening the level of protection for those who have already received shots of vaccines that are effective in preventing severe illness.

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Under the current CDC guidelines, a person is considered fully vaccinated two weeks after their final shot in a two-dose mRNA vaccine regimen or after one dose of the Johnson & Johnson vaccine. Before last week, the CDC limited its recommendation for boosters to certain groups, including people 65 and older, those who received a Johnson & Johnson shot, people 50 and older with certain medical conditions, and adults who live in long-term care settings. The agency also said adults with certain medical conditions or those who live or work in high-risk settings may get them.

Dr. Anthony Fauci, the nation’s top infectious disease expert, has made the case for boosters to be used more widely, telling Axios that he envisions boosters becoming part of the vaccination series at some point.

“In my opinion, boosters are ultimately going to become part of the standard regimen and not just a bonus,” Fauci told the publication.

Dr. Sabrina Assoumou, an infectious disease physician at Boston Medical Center and professor at Boston University School of Medicine, said she agrees, but stressed that the boosters are particularly important for certain vulnerable groups like those outlined in the CDC recommendations.

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“What I do foresee is that in the future, the mRNAs are probably going to be three shots,” Assoumou said. “If you take, for example, Pfizer — you’ll have the three weeks and then you’ll have the third shot six months later, because we know that it offers a better outcome by doing it that way.”

For those who received the one-dose Johnson & Johnson vaccine, for whom boosters are recommended by the CDC at least two months after the shot, Assoumou said she anticipates they will be considered fully vaccinated once they have had a second shot.

“I think with J&J ultimately to be considered fully vaccinated, you’re going to need that extra shot,” Assoumou said. “We’d hoped that it was only going to be just a one-shot deal, especially for people who really wanted an option with just one shot.”

Although boosters are an important tool for protection against the virus, the experts said, more focus should be paid to those who are unvaccinated, the group that is overwhelmingly more vulnerable to becoming hospitalized and dying as a result of the virus.

“I can understand why people are trying to — especially at a time when cases are going up — that they’re trying to simplify the message,” Assoumou said. “But I worry that what we should be talking about now is vaccinating the unvaccinated, and that’s not the conversation that’s happening.”

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Amid the expansion of booster shots, federal officials have not changed their definition of “fully vaccinated,” a change that would have wide ramifications as companies and government agencies require vaccinations for their workforce. An inquiry to the CDC was not returned.

Dr. Rochelle Walensky, the CDC chief, indicated in an Oct. 22 White House COVID-19 briefing that the definition of fully vaccinated may need to be updated at some point.

“Right now we don’t have booster eligibility for all people currently, so we have not yet changed the definition of fully vaccinated,” Walensky said. “We will continue to look at this. We may need to update our definition of fully vaccinated in the future.”

Whether boosters are necessary for all adults depends on what the goal is, said Dr. Andrea Ciaranello, an infectious disease physician at Massachusetts General Hospital. Boosters are necessary for certain high-risk groups, but most of those who haven’t received a booster still are well protected against severe illness after being vaccinated.

“There is, though, a real value to the boosters in preventing any sort of infection, which then prevents onward transmission to other people,” Ciaranello said. “So I think that one real potential benefit of boosters for a much wider group of adults is to try to reduce community spread. I think that is the large benefit of providing this wider range of eligibility.”

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Dr. Shira Doron, an infectious disease physician at Tufts Medical Center, said that she would like to see a clear, long-term picture from federal health officials about what the goal of the vaccination program is and added that vaccinating those who have not yet had their shots is more important for “preventing hospitalization, deaths, and changing the course of the pandemic.”

“No one thinks it’s going to dramatically change the trajectory of the pandemic, but it’s safe, so we may as well. But do we do that again in six months? That’s the question,” Doron said.

For now, it’s too early to expand the definition of fully vaccinated to include three doses, Doron added.

“We told people, take one J&J and two mRNA [vaccines] and you’re fully vaccinated, you could get back to normal, and I think it’s really hard to change the rules now,” Doron said. “I think eventually we will have to, but this feels too early to me.” ­

In September, when an FDA advisory panel recommended Pfizer’s booster for certain groups, it also voted against giving the boosters to people 16 and older. But since then, new data have emerged that make it clear that boosters increase the level of protection from the virus and are safe, Doron said.

“What we have now is real-world data not only from Israel, but from our own experience showing that the boosters do work,” Doron said. “We know that it protects against mild disease. The Pfizer clinical trial for boosters has been completed, and so we see in the most rigorous, scientific way possible — the randomized, controlled, clinical trial — that the booster dose increases the efficacy over and above two doses by a lot.”

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Amanda Kaufman can be reached at amanda.kaufman@globe.com. Follow her on Twitter @amandakauf1.