The Covid-19 vaccine developed by Novavax is highly effective against symptomatic cases of the disease, according to Phase 3 trial results announced by the company—news that comes as Covid-19 cases continue to drop precipitously nationwide.

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Details on Novavax's trial results

Novavax conducted a double-blinded, placebo-controlled trial of its vaccine in 29,960 people. During the study, 77 participants experienced confirmed cases of Covid-19, including 63 cases in the placebo group and 14 in the vaccine group. All of the cases in the vaccine group were mild, according to STAT News, and no cases in the trial were fatal.

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According to Novavax's analysis of trial results, the vaccine was 90.4% effective at preventing symptomatic cases of Covid-19 across the entire study population, and it was 91% effective in high-risk individuals, including those over the age of 65 and those with certain health conditions.

The vaccine was also found to be 93% effective against coronavirus variants of concern, including 86.3% effectiveness against the alpha variant first discovered in the United Kingdom.

According to John Moore, a virologist at Weill Cornell Medicine who volunteered in the trial, the results show that Novavax's vaccine is "comparable in potency [and] efficacy to the Pfizer and Moderna vaccines."

Side effects for the vaccine were fairly mild, according to the trial results. Some participants reported fatigue, headaches, and other symptoms. "This vaccine seems easier on the arms," Moore said.

While the Covid-19 vaccines developed by Pfizer-BioNTech and Moderna are mRNA vaccines, Novavax's vaccine is what's known as a recombinant protein vaccine, which utilizes moth cells to grow the coronavirus' spike protein, STAT News reports. The spike proteins are then turned into nanoparticles and mixed with a compound that improves immune response to the vaccine.

Novavax announced the results of the trial in a press release and said it will submit its full data for peer-reviewed publication later.

What the trial results mean for the US vaccination effort

The news comes as currently authorized Covid-19 vaccines continue to roll out across the United States.

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According to CDC, 52.4% of the U.S. population has received at least one dose of a Covid-19 vaccine while 43.4% have received all required vaccine doses. That includes 64.4% of U.S adults who have received at least one dose of a vaccine and 54.1% who have received all required doses.

Over the past two weeks, just eight states have seen their average Covid-19 case rates increase, and all of those states have vaccination rates below the national average, Axios reports. Meanwhile, the 10 states reporting the fewest Covid-19 cases per capita also have vaccination rates higher than the national average.

As the United States currently has more than enough authorized Covid-19 vaccine doses to meet demand, Novavax has said it likely won't file for FDA authorization vaccine until the end of September—although it will pursue authorization in other countries, where vaccines remain scarce, sooner.

Some say that, in the United States, Novavax's vaccine might best used as booster shots once immunity provided by the first vaccines begins to subside and more coronavirus variants emerge.

"They may be really the right ones for boosters," Luciana Borio, former acting chief scientist at FDA, said.

Novavax has said it expects to produce 100 million doses a month by the end of the third quarter of this year and should be able to increase production to 150 million a month by the end of the year.

Novavax has also promised 1.1 billion doses of its vaccine to Covax, the World Health Organization's initiative to get Covid-19 vaccines to low- and middle-income countries around the world.

"Many of our first doses will go to … low- and middle-income countries, and that was the goal to begin with," Stanley Erck, Novavax's CEO, said.

"Novavax may be used as a booster in the U.S., but it certainly will be the first vaccine a lot of people are going to see around the world," Matthew Frieman, a virologist at the University of Maryland School of Medicine, said (Branswell, STAT News, 6/14; Zimmer, New York Times, 6/14; Reyes, Axios, 6/14; Abbott, Wall Street Journal, 6/13; Ponnezhath, Reuters, 6/13; Saric, Axios, 6/13).