• Millions of Americans will be one step closer to receiving a Covid booster shot when a key FDA panel meets this week to debate extra doses of the Moderna and J&J vaccines.
• The Biden administration hopes boosting the U.S. population will ensure long-term and durable protection against severe disease.
• "Even with delta, the current vaccines are holding up quite well as far as hospitalization and severe disease," said Norman Baylor, former director of the FDA's vaccines office.

Millions of Americans will be one step closer to receiving a Covid-19 booster shot this week when a key Food and Drug Administration advisory panel meets Thursday and Friday to debate extra doses of the Moderna and Johnson & Johnson vaccines.

The FDA's Vaccines and Related Biological Products Advisory Committee meetings come less than a month after U.S. regulators authorized Covid booster shots of Pfizer and BioNTech's vaccine to a wide array of Americans, including the elderly, adults with underlying medical conditions and those who work or live in high-risk settings like health and grocery workers.

More than 7 million Americans have received a booster dose in the U.S. as of Saturday – according to the latest data available from the CDC.

Members on independent committees of the FDA and Centers for Disease Control and Prevention said at the time they were frustrated that only Pfizer recipients would be eligible to get the extra shots, leaving out millions of Americans who got Moderna's or J&J's shots.

The FDA advisory group is scheduled Thursday to discuss data on the safety and effectiveness of a Moderna booster shot in adults. On Friday, the committee is expected to debate J&J booster shots for adults. The FDA could make a final decision within days of the meetings, handing it off to the CDC and its vaccine advisory committee to make their own decision.

The CDC's next vaccine advisory meeting is scheduled for Oct. 20 to Oct. 21 where it's expected to discuss the boosters.

The FDA meeting comes after average daily Covid cases in the U.S. fell below 100,000 last week with more than 56% of the population fully immunized against the virus and the pandemic showing signs of easing. Getting vaccinated, receiving booster shots and avoiding large gatherings are crucial ways to mitigate a possible surge in cases over the holidays, health experts say.

The Biden administration hopes boosting the U.S. population will also continue to ensure long-term and durable protection against severe disease, hospitalization and death as the fast-moving delta variant spreads.

The strain led to a surge in hospitalizations in the U.S., mainly among the unvaccinated. Still, some vaccinated Americans have suffered so-called breakthrough infections and just over 19,000 of them – less than 1% – have been hospitalized or died with Covid as of Sept. 20, according to data compiled by the CDC.

"Even with delta, the current vaccines are holding up quite well as far as hospitalization and severe disease," said Norman Baylor, former director of the FDA's vaccines office. "It's the infections that seem to be a concern."

Last month, Moderna said a third shot at half the dosage used for the first two jabs was safe and produced a stronger immune response than what was seen after the second dose in its phase three clinical trial.

J&J said last month a second dose of its single-shot vaccine was safe and boosted protection against symptomatic infection from around 70% to 94% when administered two months after the first dose in the United States.

The FDA could authorize Moderna and J&J booster shots under the same criteria as Pfizer or perhaps change course and broaden the number of Americans eligible to receive extra shots, Baylor said in a phone interview.

"The question is: does everybody need a booster right now?" said Baylor, now president of Biologics Consulting Group.

Committee members will have to debate whether its safe and effective for J&J recipients to get a second dose, Baylor said. He added he doesn't expect any trouble authorizing third doses of Moderna's vaccine as it uses mRNA technology, which was also used to develop Pfizer's vaccines.

"If I were at the FDA in my old position, I probably would not have taken the Moderna to the advisory committee because it's in the same class as Pfizer," he said.

The administration's communication on Pfizer booster shots was already confusing and "very damaging" in terms of public perception, said Dr. Isaac Bogoch, an infectious disease specialist at the University of Toronto.

"From the outside looking in, it looks like a bit of a free-for-all," Bogoch said. "Like, yeah there's some loose guidance in the United States. But it basically looks like anyone can go into any pharmacy and get a booster shot and say you know what I smoke or I'm obese or I'm a health-care worker."