A federal advisory committee on Tuesday will vote on whether regulators should authorize a Covid-19 vaccine made by Novavax, an early beneficiary of the government’s Operation Warp Speed program.The experts to the Food and Drug Administration, whose meeting is scheduled to begin at 8:30 a.m. Eastern, will base their recommendation on the company’s clinical trial data, which is strong. But before the agency could authorize the shots, the F.D.A. would also need to sign off on Novavax’s manufacturing process, which has stumbled again and again over the course of two years.If the F.D.A. authorizes the Novavax two-dose vaccine, it would become the fourth shot to win clearance for adults in the United States. But even if the company does get the green light, it is unclear when or how widely the vaccine might be available. Shots from Pfizer-BioNTech, Moderna and Johnson & Johnson have been authorized for well over a year, and the country is not short of doses. And in a number of countries where Novavax has already earned authorization, uptake has been low.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, including those that prefer a non-mRNA option.” (Pfizer and Moderna’s shots are made with mRNA.)The Novavax vaccine contains nanoparticles made up of proteins from the surface of the coronavirus, a fundamentally different design than the three authorized shots.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.“These events raise the concern for a causal association with this vaccine,” the F.D.A. documents stated.“We believe there is insufficient evidence to establish a causal relationship,” Novavax said in a statement. “We will continue to monitor all adverse events, including myocarditis and pericarditis.”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.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.Demand for the vaccine also appears to be tepid in other countries. Novavax has shipped 42 million doses through the first quarter of this year, to 41 countries. In its briefing documents, the F.D.A. said that Australia, Canada, the European Union, New Zealand and South Korea provide data on how many people have actually received the vaccine. The grand total in these countries came to fewer than 750,000 doses.When contacted for comment, Novavax did not provide a total number of doses administered worldwide in other countries, such as India.As part of its initial support for Novavax’s research, the United States agreed to buy 110 million doses of the vaccine if it won authorization. But two years later, with the country already flush with effective mRNA vaccines, the government has little need for more.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 sold in the United States.The F.D.A. said in its briefing documents that testing and submission of manufacturing data on the vaccine “were still in process” at the time of its review.In an interview, Stanley Erck, the chief executive of Novavax, said that the company was in discussions with the government about how many doses it will supply. “I anticipate that there will be several million doses coming into the U.S. within weeks of the E.U.A.,” he said, referring to an emergency use authorization.

A highly anticipated study of Pfizer’s Covid pill confirmed that it helps stave off severe disease, the company announced on Tuesday.Pfizer also said its antiviral pill worked in laboratory studies against the Omicron variant, which is surging in South Africa and Europe and is expected to dominate U.S. cases in the weeks ahead.“We are confident that, if authorized or approved, this potential treatment could be a critical tool to help quell the pandemic,” Albert Bourla, Pfizer’s chief executive, said in a statement.Last month, Pfizer asked the Food and Drug Administration to authorize the pill, known as Paxlovid, based on a preliminary batch of data. The new results will undoubtedly strengthen the company’s application, which could mean that Americans infected with the virus may have access to the pill within weeks.In Tuesday’s announcement, Pfizer said that if given within three days of the onset of symptoms, Paxlovid reduced the risk of hospitalization and death by 89 percent. If given within five days, the risk was reduced almost as much, to 88 percent.The results, based on an analysis of 2,246 unvaccinated volunteers at high risk of severe disease, largely match the company’s initial, smaller analysis of the clinical trial, released last month.Pfizer said that 0.7 percent of patients who received Paxlovid were hospitalized within 28 days of entering the trial, and none died. By contrast, 6.5 percent of patients who received a placebo were hospitalized or died.Pfizer also released preliminary data from a separate trial looking at people with a lower risk. These volunteers including vaccinated people who carried a risk factor for severe disease, as well as unvaccinated patients with no risk factors.Among this group of 662 volunteers, Paxlovid reduced the risk of hospitalization and death by 70 percent, the company said.Mikael Dolsten, the chief scientific officer of Pfizer, was exuberant about the results after having overseen the development of the drug since the spring of 2020, with more than 200 company scientists crafting the molecule and then testing it in animals and people.While the drug was in development, Dr. Dolsten held out hope that it might be 60 percent effective. Its true potency left him stunned. “We really hit the top of the board,” he said in an interview.In both trials, most of the volunteers were infected with the Delta variant. But Pfizer said on Tuesday that in laboratory experiments, Paxlovid also performed well against the highly mutated Omicron variant. The drug jams into one of Omicron’s key proteins — called a protease — just as effectively as it does with other variants, Pfizer found.Pfizer’s good news came as its rival, Merck, awaited word on authorization of its own antiviral pill, known as molnupiravir. In October, Merck and its partner Ridgeback Biotherapeutics announced that the pill reduced the risk of hospitalization and death from Covid-19 by 50 percent if taken within five days of the onset of symptoms.The Coronavirus Pandemic: Key Things to KnowCard 1 of 4U.S. nears 800,000 Covid deaths.