Novavax received significant federal funding to produce the vaccine that was approved by the FDA on Wednesday. The vaccine will be a new choice for Americans.

The vaccine has overcome manufacturing problems to become the fourth shot in the United States. Advisers to the Centers for Disease Control and Prevention are expected to discuss who should get the Novavax vaccine.

The two-dose vaccine was authorized as a primary immunization series for adults, rather than a booster, which will limit its market initially. The Biden administration said earlier this week that it would buy enough vaccine to cover 1.6 million people in the US. The government said that Novavax was expected to finish its quality testing in the next few weeks.

Novavax wants to appeal to people who have rejected the shots from Pfizer-bioNTech and Moderna. More than 20% of people in the United States have not received a single dose of Covid vaccine.

Novavax's vaccine does not work the same way as a mRNA vaccine. It causes an immune response with particles from the coronaviruses that cause Covid-19 The world has used similar vaccines for a long time.

It is not clear if the company's prediction for the United States will hold up due to modest demand for the Novavax shot in other wealthy countries. Between December and June 30 of this year, only 12.6 million doses of Novavax were given out in Europe. More than a billion doses of Pfizer-bioNTech and Moderna vaccine have been distributed in Europe.

According to a Morning Consult poll, Novavax may face the same lack of enthusiasm in the US. A majority of unvaccinated people said they would probably or definitely get a vaccine based on a specific type of animal.

The vaccine is linked to an elevated risk of heart inflammation called myocarditis and pericarditis. Six cases of the side effect were identified by F.D.A. scientists.

After they were put into large-scale use, the link between Moderna and Pfizer- BioNTech's vaccines and elevated risk of these conditions emerged. There was a warning in their packaging.

Novavax had several vaccines in the research portfolio, but no approved products before the Pandemic. The federal government's 2020 campaign to develop coronaviruses vaccines picked it out for support. Up to 100 million doses of the vaccine were to be purchased by the program.

The shot was not available for the initial surge of vaccinations in the United States due to manufacturing delays.

The manufacturing troubles have continued to bother the company. After an F.D.A. advisory committee recommended authorizing the vaccine in June, the agency needed more time to sign off on Novavax's manufacturing process. The world's largest vaccine maker is making Novavax's vaccine.

Novavax's vaccine was found to be very protective against certain infections. The Omicron variant has evaded some of the protection afforded by authorized vaccines from other companies.

Novavax is working on a vaccine that targets Omicron and its subvariants. According to preliminary data from laboratory and animal studies, a booster shot aimed at a previous Omicron subvariant creates strong immune responses. The company expects to have the results from the trial in September, with the shots ready in the last three months of this year.

The company plans to speed up its research on shots for two newer versions of Omicron.

Novavax's shot works well as a booster and the company is expected to get authorization soon. It is possible that the company will be able to attract people who want to switch to a new vaccine.

John Moore thought that Novavax was an excellent vaccine but was not sure if an Omicron-based booster would provide the same protection as the original version. He said there wasn't enough information.

According to Dr. Moore, some people might switch to Novavax for a booster this fall because of the low incidence of side effects in clinical trials. He volunteered in a Novavax trial. He said that the only way to know which arm he had the needle in was to use Band-Aid.

If Novavax is approved for a booster, Dr. Moore would return for a second shot.