The Maryland-based biotech company Novavax reported Monday that its experimental Covid-19 vaccine is safe and 100 percent effective against moderate to severe disease.
The results are from the company's Phase 3 clinical trials conducted in the U.S. and Mexico. The company has already completed a Phase 3 trial in the U.K., but the U.S. trial results are required to apply for emergency use authorization in this country.
Novavax said in a statement that it plans to apply to the Food and Drug Administration for authorization in the third quarter. That would add a fourth vaccine to the U.S. arsenal.
But the Biden administration has already secured enough doses of the three vaccines currently available to vaccinate the U.S. population, and vaccine uptake in the U.S. has slowed in recent weeks, further weakening the need for additional Covid-19 vaccines.
While it is unlikely that Novavax's shots will be used as a first line of defense in the U.S., they could still be used in the coming months or even years, the company said.
"I think particularly in the United States, our vaccine is going to be most importantly used as a booster vaccine," Stanley Erck, Novavax's chief executive officer, said Monday during a call with investors.
Other parts of the world remain vulnerable and in urgent need of Covid-19 vaccines. President Joe Biden and other leaders pledged at the Group of Seven summit over the weekend to donate 1 billion vaccine doses to lower-income countries.
Indeed, "a lot of our first doses are going to go into low- and middle-income countries, as they should," Erck said.
"We need more manufacturers producing more vaccines," said Dr. William Schaffner, an infectious diseases expert at Vanderbilt University Medical Center in Nashville, Tennessee. "The global need for them is vast."
Dr. David Hirschwerk, an infectious disease specialist at the Northwell Health System in Manhasset, New York, agreed. "The more ways that we have at getting at this virus, and the more ways that we have at providing protection to people, the better off we are," he said.
The Novavax vaccine is given in two doses, 21 days apart. The Phase 3 trial included nearly 30,000 participants in the U.S. and Mexico, and it included underrepresented minority groups, as well as populations at high risk for Covid-19, the company said in a statement.
By the end of the trial, there were 77 cases of Covid-19: 63 in the placebo group and 14 in the vaccine group, for an overall efficacy of 90 percent, the company said. All cases in the vaccine group were mild, meaning the vaccine was 100 percent effective against moderate to severe illness. (The company's findings were presented in a news release and still must be submitted for peer review.)
Novavax said the vaccine was 93 percent effective against what the Centers for Disease Control and Prevention has defined as variants of concern or variants of interest, including the Alpha variant, or B.1.1.7, first found in the U.K., which was the predominant variant seen in the U.S. trial.
The variants first identified in Brazil, South Africa and India also accounted for a very small proportion of cases.
Those particular variants will be critical to study moving forward, said Dr. Gregory Poland, director of the Mayo Clinic's Vaccine Research Group in Rochester, Minnesota.
"Those variants elsewhere will soon be variants here," he said. "The Delta variant was was discovered in India is now one of the most common variants circulating the U.K. Given its much higher infectivity, it's going to become a dominant variant — probably this fall — in the U.S."
Download the NBC News app for full coverage of the coronavirus outbreak
Novavax was one of five drugmakers to receive funding from the Trump administration's Operation Warp Speed, an initiative to develop Covid-19 vaccines. Novavax's vaccine would be the third Operation Warp Speed candidate to get the green light from the FDA, along with those of Moderna and Johnson & Johnson. (Pfizer-BioNTech didn't get funding from the program for its vaccine.)
The Novavax vaccine differs slightly from the other vaccines in use. The Pfizer, Moderna and Johnson & Johnson vaccines all work by providing genetic instructions for the body to build the coronavirus's spike protein, which the immune system learns to recognize and fight. The Novavax shot skips the instructions and delivers the spike protein directly to the body.
Many well-known vaccines use a similar approach — delivering a specific part of the pathogen to the body to learn to recognize — including the hepatitis B vaccine, the HPV vaccine and the shingles vaccine. The Novavax vaccine can be stored in standard refrigerator temperatures.
As of Sunday, more than 143 million people in the U.S. had been fully vaccinated, according to the CDC.