A federal advisory committee on Tuesday voted to recommend that regulators authorize a Covid-19 vaccine made by Novavax, an early beneficiary of the government’s Operation Warp Speed program.

If the Food and Drug Administration accepts the panel’s recommendation on the Novavax two-dose vaccine, it would become the fourth shot to win clearance for adults in the United States. But before the agency could authorize the shots, the F.D.A. would need to sign off on Novavax’s manufacturing process, which has stumbled again and again over the course of two years.

Those ongoing issues are likely to mean the vaccine would not be available for weeks, in contrast to the already cleared Covid vaccines that became available just days after the same committee endorsed those shots. The Centers for Disease Control and Prevention must also recommend use of the shots before they could become available.

The federal government is coordinating with Novavax to receive “a limited quantity of vaccine” if it is authorized and recommended in the United States, Jorge Silva, a spokesman for the Department of Health and Human Services, said in an email. “We remain committed to ensuring that any American who wants a vaccine can get one.”

The government would most likely buy several million doses, according to two people familiar with the plan. As part of its initial support for Novavax’s research in 2020, the United States had agreed to buy 110 million doses of the vaccine if it won authorization. But two years later, with the country already flush with effective vaccines, the government has little need for more.

Shots from Pfizer-BioNTech, Moderna and Johnson & Johnson have been authorized for well over a year. And in a number of countries where Novavax has already earned authorization, uptake has been low.

The Novavax vaccine contains nanoparticles made up of proteins from the surface of the coronavirus, a fundamentally different design than the three shots available in the United States. Pfizer-BioNTech and Moderna’s shots are made with mRNA, while the shot from Johnson & Johnson, the use of which has been limited in the United States, uses a non-mRNA approach.

At Tuesday’s meeting, the advisory committee’s 22 voting members nearly unanimously endorsed Novavax’s shot, with 21 votes in favor of authorization and one abstention.

Dr. Peter Marks, who oversees vaccine regulation for the F.D.A., said there was a need for alternative vaccine options. “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 lifesaving medical products is something that we feel we are compelled to do,” he said.

Addressing the committee, Martha Dawson, the president of the National Black Nurses Association, said that some patients will feel more comfortable using protein-based vaccines, a technology that has been in use for decades. “I encourage the F.D.A. to give us another, more traditional medical intervention in this fight,” she said.

In clinical trials, the Novavax vaccine was found to have an efficacy of 90.4 percent at preventing mild, moderate or severe infection with older variants of the virus. None of the volunteers who got the vaccine experienced moderate or severe infection, translating to an efficacy of 100 percent.

The trial took place before the rise of the Delta and Omicron variants, which have evaded some of the immunity from other vaccines.

In briefing documents released on Friday, F.D.A. scientists identified six cases of myocarditis and pericarditis, forms of heart inflammation, in about 40,000 trial volunteers. The F.D.A. documents said that the cases raised concern that the vaccine was the cause and that the rates of the problems could turn out to be higher than with mRNA vaccines.

Moderna and Pfizer-BioNTech did not find any cases of myocarditis or pericarditis in their initial clinical trials. But after authorization, once the vaccines were given to millions of people, they were both found to create a small extra risk of myocarditis in boys and young men.

In their presentation on Tuesday, Novavax officials defended their vaccine against those concerns. Their analysis found that myocarditis and pericarditis cases were balanced across the group of volunteers that received the vaccine and the group that received a placebo. In the real world, there were reports of one case of likely myocarditis and eight cases of likely pericarditis out of 744,000 doses given in rich countries that have authorized the vaccine, the company said.

“We believe that the totality of the clinical evidence here is not enough to establish an overall causal relationship with the vaccine,” said Dr. Denny Kim, Novavax’s chief safety officer.

The Novavax vaccine has been authorized in dozens of countries, including India, South Africa and Britain, and has also received clearance from the European Union and World Health Organization.

But the vaccine is falling far short of initial hopes, both in terms of the number of vaccines distributed around the world and the number of people who are receiving them.

In February 2021, Novavax pledged 1.1 billion doses to Covax, the United Nations program supplying shots to developing countries. But because of the delays, Covax has not yet ordered any doses from Novavax. The company said it has shipped 42 million doses through the first quarter of this year, to 41 countries.

Novavax had planned for factories around the world to manufacture its vaccine, but the company had trouble scaling up production and was slow to demonstrate that its process met F.D.A. standards. The Serum Institute of India, the world’s largest vaccine producer, is now manufacturing Novavax’s vaccine and would be the supplier of any doses initially sold in the United States.

The F.D.A. said in its briefing documents that Novavax must demonstrate that the product that Serum would bring to the U.S. market is of the same quality as the vaccine the company used in the large-scale clinical trial at the center of its application. The agency said that testing and submission of manufacturing data on the vaccine “were still in process” at the time of its review.

Novavax has said that Serum’s plant has successfully completed an F.D.A. inspection and that it submitted updated manufacturing data to the agency last week.

F.D.A. reviewers also said in the briefing documents that they could not evaluate certain data from three of Novavax’s overseas trials because the company used a different manufacturing process for those studies than it did for its main trial in the U.S. and Mexico.

Dr. Marks of the F.D.A. said that the agency takes manufacturing “very seriously,” adding: “We don’t benchmark ourselves against other countries.”

While the committee’s recommendation only applied to primary immunizations for adults, Novavax plans to also seek authorization for adolescents and children. The vaccine is authorized for adolescents in India and Thailand.

The company also plans to seek authorization for its vaccine as a Covid booster. The company has run trials showing that a booster produces a large increase in antibodies. Last week, the company also began a trial in Australia to test a booster tailored specifically for the Omicron variant, which has become dominant worldwide.

The F.D.A. panel will meet later this month to consider whether the existing vaccines should be updated to more effectively target newer virus variants.

Sharon LaFraniere and Noah Weiland contributed reporting.