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GAITHERSBURG, Md. — Another COVID-19 vaccine is getting closer to the finish line, as Novavax said Thursday its shot prevented hospitalizations and deaths in studies in Britain and South Africa where mutated versions of the virus are spreading.

The American biotech company said its vaccine candidate, called NVX-CoV2373, demonstrated 100% protection against severe disease, including all hospitalization and death.

In a study of 15,000 people in Britain, the Novavax vaccine was about 90% effective overall against mild, moderate or severe COVID-19, the company said. Of 106 illnesses confirmed, 10 were among people given the vaccine and 96 were among people given dummy shots.

“The complete analysis shows that vaccine-induced protection began 14 days after dose 1 — although increased efficacy was observed seven days after dose 2, the primary endpoint for the study,” according to Novavax.

Only five of the illnesses were severe, all in the placebo group. Four of those were caused by an easier-to-transmit coronavirus variant first discovered in Britain. Novavax determined the vaccine was 96% effective against symptomatic illness caused by the original virus — and 86% effective against that mutated version.

In South Africa, an even more worrisome variant is spreading widely. Novavax studied nearly 3,000 people there, some who have HIV. The company said its vaccine was 55% effective against symptomatic COVID-19 in HIV-negative volunteers. Like in Britain, the only severe illnesses occurred in study participants given dummy shots.

“The bigger picture is our vaccine works against variants,” said Novavax CEO Stanley Erck.

Erck said he expected to file an application with British health authorities early in the second quarter for widespread use of the vaccine. The company also is awaiting results from a 30,000-person U.S. study.

As of March 12, three vaccine candidates are approved for use in the United States: Moderna, Pfizer-BioNTech and Johnson & Johnson, the last of which only needs one dose to be effective.