FDA on Thursday authorized third doses of Pfizer-BioNTech's and Moderna's Covid-19 vaccines for some immunocompromised people, and CDC's Advisory Committee on Immunization Practices (ACIP) on Friday recommended the extra doses for those individuals.

Some experts worry, however, that the move will open the floodgates for healthy people to get extra shots they don't qualify for.

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FDA authorizes booster shots, and CDC recommends them

On Thursday, FDA updated the emergency use authorization for Pfizer-BioNTech's and Moderna's vaccines to incorporate the extra doses. The expanded authorization applies to those who have received solid organ transplants and other patients with similarly compromised immune systems, which includes about 3% of Americans, the New York Times reports.

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Studies have found that the initial two-dose regiment of the Moderna and Pfizer-BioNTech Covid-19 vaccines is less effective in the immunocompromised.

On Friday, CDC's ACIP provided a more detailed list of individuals for whom it recommends an extra dose. That list includes those who:

• Are receiving active cancer treatment for tumors or cancers of the blood;
• Have received an organ transplant and are taking medicine to suppress the immune system;
• Have received a stem cell transplant within the last two years or are taking medicine to suppress the immune system;
• Have moderate or severe primary immunodeficiency;
• Have advanced or untreated HIV infection; or
• Are undergoing active treatment with high-dose corticosteroids or other drugs that may suppress the immune response.

"If I was someone who was on one of the medications that was on the CDC list, you know, I would almost consider myself unvaccinated at this point," David Karp, head of the Division of Rheumatic Diseases at UT Southwestern Medical Center, said.

"For this group of patients, you know, a third shot is going to improve their response to the vaccine and therefore lessen their chances of either contracting the disease or having a more serious disease," he added.

Patients who qualify for an extra dose won't need permission from their doctor to receive it, CDC officials said. They will need only to state they meet the eligibility requirements to receive the dose.

Are boosters coming for the rest of the population?

Andrew Badley, chair of the Mayo Clinic's Covid-19 research task force, said the authorization of additional doses for the immunocompromised is "not the end of the story."

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"The question that's on everyone's mind—and studies are underway is—is there a role for booster vaccines to augment waning immunity" for others, he said.

Francis Collins, director of NIH, said on Sunday the Biden administration is looking into the data on whether boosters will be necessary for the broader population.

Stephen Hoge, president of Moderna, said on Sunday that some breakthrough infections resulting from the delta variant are emerging six to nine months after inoculation. "I think that suggests we are going to need booster vaccines to get through the winter," he said.

Some experts warn of a potential rush for unauthorized booster shots

Some experts expressed concern that FDA's expanded authorization will make it easier for those who don't qualify for extra shots to get them, since the new policy relies on patients to self-attest to qualifying conditions.

"I worry very much that this is going to lead to vaccination chaos," Michael Osterholm, director of the University of Minnesota's Center for Infectious Diseases Research and Policy, said.

Currently, CDC has said it's aware of at least 1.1 million people who have gotten an extra dose of a Covid-19 vaccine.

"Are people going to game the system, who just want a third dose?" Jason Goldman, who represents the American College of Physicians on ACIP, said. "I'm already seeing it with patients, after FDA's announcement, calling my office, wanting me to give them a letter to justify that they need a third dose when they are not immunocompromised."

Osterholm said he "can only imagine how many more people" will try to get an extra dose. "I could easily see several million people wanting to get that additional dose," he said. (Weiland/LaFraniere, New York Times, 8/12; Weiland, New York Times, 8/13; Wroth et al., NPR, 8/14; Reed, Axios, 8/16; Branswell, STAT News, 8/15; AP/Modern Healthcare, 8/15)