Most of the FDA's Vaccines and Related Biological Products Advisory Committee voted "yes" in response to a question of whether the benefits of Novavax's vaccine, given as a two-dose primary series, outweigh its risks in people 18 and older, based on available evidence. Twenty-one members voted yes, one abstained, and none voted no.

If the full FDA gives the vaccine the green light, it will become the fourth Covid-19 vaccine authorized in the United States.

Novavax's vaccine is made using small laboratory-built pieces of the coronavirus to stimulate immunity. This protein-based approach is a more traditional one for vaccine development than the mRNA vaccines from Pfizer/BioNTech and Moderna.

Committee member Dr. Jay Portnoy, a professor of pediatrics at the University of Missouri-Kansas City School of Medicine, said he sees the vote as an opportunity.

"This is a different technology. It's a more traditional protein-based vaccine," Portnoy said. "The vaccine deserves the opportunity to be given and studied."

"Certainly, the benefits outweigh the risks for a primary series," committee member Dr. Michael Nelson, asthma, allergy and clinical immunology division chief at the University of Virginia School of Medicine, said of the vote.

"I think this group was in full recognition that this is probably a three-dose series and then will need to accumulate data supporting the need for booster doses and subsequent doses to probably make it a three-dose vaccine," he said, hinting at how discussions might continue for the vaccine to be used as a booster shot.

Ahead of Tuesday's meeting, an FDA briefing documentfound that although most adverse reactions to the vaccine were mild to moderate and lasted just a few days, myocarditis and pericarditis -- inflammation of the heart muscle and inflammation of tissue surrounding the heart -- happened in six people after vaccination. For five of them, the inflammation emerged within just two weeks of getting the vaccine. In one person, it happened 28 days later.

The cases were similar to myocarditis after the mRNA Covid-19 vaccines developed by Pfizer/BioNTech and Moderna, and they raise "concern for a causal relationship" with Novavax's vaccine, according to the FDA document.

Novavax said in a statement that there wasn't a substantial difference in rates of myocarditis between clinical trial participants who got the vaccine (0.007%) and those who got a placebo (0.005%).

Novavax seeks US authorization

In November, Indonesia became the first country to grant emergency use authorization of Novavax's vaccine. It has also been authorized in the European Union, the United Kingdom, Canada, South Korea, Australia, India, the Philippines and New Zealand, among other countries.

In late January, Novavax announced that it had submitted a request for the FDA to authorize its coronavirus vaccine for emergency use.

Novavax is prepared to ship doses of its vaccine from the Serum Institute in India when the FDA authorizes it.

"Our hope is that the FDA takes the recommendation of this VRBPAC committee ... along with all the manufacturing data that we've given them and with the results of their inspection of our plant in India, and can reach a decision. We hope that's soon," Stanley Erck, Novavax's president and chief executive officer, told CNN on Tuesday.

The company's first shipment to the United States will be "a few million" doses, he said.

As for who could receive the vaccine, "there are tens of millions of people who have not had their primary vaccine for one reason or another," Erck said. "That's one market for us."

He added that other markets for the vaccine include children and, eventually, people who need booster doses to maintain protection against Covid-19.

Novavax's request for authorization was based on data including the results of two large clinical trials that demonstrated an overall efficacy of about 90% and a "reassuring safety profile," according to the company. The trials were conducted before the Omicron coronavirus variant dominated in the United States.

"The Advisory Committee's positive recommendation acknowledges the strength of our data and the importance of a protein-based COVID-19 vaccine developed using an innovative approach to traditional vaccine technology," Erck said in a statement after Tuesday's meeting.

"We have heard in today's VRBPAC meeting the significant support for our vaccine from physicians, healthcare organizations, and consumers who are eagerly anticipating a protein-based vaccine option," he said. "We look forward to the FDA decision."

Overall, the uptake of Covid-19 vaccinations -- especially booster doses -- in the United States has been slow, and one FDA official described it as a "very serious" problem in Tuesday's meeting.

"We do have a problem with vaccine uptake that is very serious in the United States, and anything we can do to get people more comfortable to be able to accept these potentially life-saving medical products is something that we feel we are compelled to do," said Dr. Peter Marks, director of the Center for Biologics Evaluation and Research.

Dr. Eric Rubin, editor-in-chief of the New England Journal of Medicine and a member of VRBPAC, asked in the meeting why there is a need for another Covid-19 vaccine in the United States when three have been authorized or approved: those from Pfizer/BioNTech, Moderna and Johnson & Johnson's Janssen.

"The Janssen vaccine is currently not being used as a frontline vaccine the same way as the mRNA vaccines, which leaves the issue of vaccines for those who might not want to take an mRNA vaccine because of concerns they might have," Marks responded, referring to the vaccines developed by Pfizer/BioNTech and Moderna.

"Having a protein-based alternative may be more comfortable for some in terms of their acceptance of vaccine," Marks said.

More than two-thirds of the US population is fully vaccinated with at least their initial series, but Novavax officials have said that they plan to seek authorization of the vaccine for use as a booster dose too -- and it can be used in people who got another vaccine type as their initial series.