FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) on Tuesday recommended authorization of Novavax's Covid-19 vaccine—a move that brings Americans one step closer to a fourth Covid-19 vaccine option."

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FDA scientists evaluate the effectiveness of Novavax's vaccine candidate

FDA on Friday detailed their analysis of Novavax's Covid-19 vaccine, known as NVX-CoV2373, in briefing documents released ahead of the agency's VRBPAC meeting on Tuesday.

Unlike Pfizer-BioNTech and Moderna's mRNA vaccines and Johnson & Johnson's adenovirus vaccine, Novavax's vaccine is considered more traditional, and contains nanoparticles made up of proteins from the surface of the coronavirus. The vaccine requires two shots, 21 days apart, and is already authorized for use in several other countries.

In its analysis, FDA scientists acknowledged that Novavax's vaccine was effective at preventing disease, noting the vaccine was found to be 90.4% effective at preventing coronavirus infection with older variants of the virus. However, FDA questioned its efficacy against currently circulating strains, largely because the study was conducted before the delta and omicron variants emerged.

In addition, FDA's scientists raised concerns about the potential risk of myocarditis and pericarditis associated with the vaccines. Notably, both conditions have also been associated with Pfizer-BioNTech and Moderna's vaccines.

The agency's review noted several instances in which individuals who received the vaccine faced an increased potential risk of the heart conditions, especially within seven days of the second shot, Axios reports. Of those, four of the instances occurred in young men—a population known to face a higher risk of mRNA vaccine-related myocarditis.

According to FDA, the identification of multiple vaccine-associated myocarditis/pericarditis cases in Novavax's trial safety database raises concern. The agency's scientists noted that while myocarditis has been identified as a potential risk following vaccination with the mRNA vaccines, it was not identified before the mRNA vaccines were authorized.

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

On Friday, FDA said that the authorization of the Novavax vaccine would also depend on information about the company's manufacturing processes.

"Testing and submission of manufacturing and product information for the NVX-CoV2373 product intended for use under [emergency use authorization] (EUA) were still in process at the time of this review," the FDA scientists wrote.

VRBPAC recommends vaccine to FDA

On Tuesday, VRBPAC voted 21-0 with one abstention in favor of Novavax's vaccine receiving an EUA. FDA does not have to follow VRBPAC's advice, but it generally does, meaning the vaccine could be authorized for use in the United States in the coming weeks, STAT news reports.

However, it's unclear exactly when doses will become available, as FDA is still reviewing data regarding the vaccines' manufacturing.

Bruce Gellin, chief of global public health strategy at the Rockefeller Foundation, abstained but said he was giving the vaccine a "conditional yes." Gellin said the vaccine was shown to be generally safe and effective in trials, but added that "we don't know whether that is true today."

Gellin said his vote reflected "insights into [the vaccine's] performance, not just the science that tells us about its promise," adding that "this vaccine has incredible potential and a lot has been learned about it that we didn't hear about."

Because Novavax's vaccine uses more traditional technology, FDA advisors, as well as independent outside experts, have noted that this could make those who are skeptical of mRNA vaccines and therefore remain unvaccinated more comfortable.

Peter Marks, director of FDA's Center for Biologics Evaluation and Research, said the vaccine will fill "an unmet need."

"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.

"Having a protein-based alternative may be more comfortable for some in terms of their acceptance of vaccines," he added.

Eric Rubin, an infectious disease specialist at Brigham and Women's Hospital, said it's "disappointing" there isn't "more updated information" on Novavax's vaccine "because we're looking at the efficacy against strains that don't exist anymore." Still, Rubin said the case for the vaccine was "pretty compelling" given that some who have avoided receiving an mRNA vaccine have shown interest in Novavax's vaccine.

Separately, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, agreed, saying, "We all know that there are certain people in the population who are still concerned about a vaccine that is relatively new in the arena of vaccinology. And they may want a more classical vaccine that we have years and years of experience with."

Still, some experts remain skeptical that those who remain unvaccinated would be persuaded by the Novavax vaccine.

"I'm not sure I buy into that, unfortunately," said Saad Omer, who studies vaccines at Yale University. "It's not like there's a huge chunk of people just waiting for something other than an mRNA vaccine and will just get vaccinated. I don't think so."

"Based on the efficacy estimate in the clinical trial of this vaccine, it is more likely than not that the vaccine will provide some meaningful level of protection against COVID-19 due to Omicron, in particular against more severe disease," FDA scientists wrote. (Weintraub, USA Today, 6/7; Zimmer/Robbins, New York Times, 6/8; Herper, STAT News, 6/3; Bettelheim, Axios, 6/3; Stein, "Shots," NPR, 6/3; Walker, MedPage Today, 6/7; Johnson/McGinley, Washington Post, 6/7; Neergaard, Associated Press, 6/7; Whyte, Wall Street Journal, 6/7; Branswell, STAT News, 6/7)