The US Food and Drug Administration on Wednesday issued a long-awaited authorization for Novavax's COVID-19 vaccine. It is the fourth COVID-19 vaccine to gain authorization in the US, but it's the first to use a more conventional protein-subunit design.

For now, the two-dose vaccine is mainly aimed at the roughly 72 million Americans who have yet to receive one dose of a COVID-19 vaccine. The FDA's emergency use authorization only allows for its use as a primary series, not a booster for those already vaccinated. Though Novavax is expected to seek booster authorization later, the company and the FDA hope that the vaccine's traditional formulation will entice vaccination holdouts now, particularly as BA.5 sweeps the country.

Some consider the vaccine's protein-subunit design to be a more tried-and-true design relative to the newer mRNA-based platform used in the leading COVID-19 vaccines made by Pfizer-BioNTech and Moderna. While mRNA-based vaccines made their public debut during the pandemic, protein-subunit-based vaccines were already in use against various diseases, including hepatitis B, flu, pertussis (whooping-cough), and meningococcal infections.

To fight COVID-19, the Novavax vaccine directly delivers the SARS-CoV-2 spike protein, which is manufactured at scale in insect cells. The vaccine also includes an adjuvant, which is an additive that enhances immune responses. In this case, the adjuvant involves saponin extracts from the Chilean soapbark tree previously used in FDA-approved vaccines.

Long-awaited option

In a meeting of FDA advisers last month, the agency's top vaccine regulator, Peter Marks, expressed the need for more vaccine options in the US. "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," Marks said. As such, many experts were eager to see the Novavax vaccine authorized. But, the vaccine, which has been in development for two years, had been significantly delayed by a string of manufacturing setbacks that have only recently been cleared up.

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Still, in the June meeting, FDA advisers voted nearly unanimously in favor of the FDA authorizing the vaccine. In a large trial of over 25,000, the vaccine appeared to be 90.4 percent effective against COVID-19, though the trial was conducted before the delta and omicron variants emerged. The vaccine also appears generally safe, though it does come with an increased risk of myocarditis and pericarditis (inflammation of the heart and surrounding tissue). Ultimately, 21 of 22 FDA advisers voted in favor of authorization, while one expert abstained, citing the lack of variant-specific efficacy data.

"Today's authorization offers adults in the United States who have not yet received a COVID-19 vaccine another option that meets the FDA's rigorous standards for safety, effectiveness, and manufacturing quality needed to support emergency use authorization. COVID-19 vaccines remain the best preventive measure against severe disease caused by COVID-19," FDA Commissioner Robert Califf said in a statement on Wednesday. "And I encourage anyone who is eligible for, but has not yet received a COVID-19 vaccine, to consider doing so."

The authorization lands as federal officials are renewing efforts to increase vaccination rates, which have largely stagnated. Last week, Novavax announced that the US government had signed a deal to buy 3.2 million doses. But, before Novavax shots can begin going in arms, the Centers for Disease Control and Prevention will need to sign off. CDC advisers are expected to convene next week to discuss the vaccine.