The company said the vaccine candidate had a final efficacy of 86.3% against the fast-spreading UK variant of COVID-19. The UK study enrolled more than 15,000 participants.
The vaccine candidate had even higher effectiveness against original COVID-19, with 96.4% efficacy. In both cases the vaccine candidate provided “100% protection against severe disease, including all hospitalization and death,” the company said in a statement.
"We are very encouraged by the data showing that NVX-CoV2373 not only provided complete protection against the most severe forms of disease, but also dramatically reduced mild and moderate disease across both trials. Importantly, both studies confirmed efficacy against the variant strains," said Stanley C. Erck, president and CEO of Novavax in the statement.
Shares of Novavax soared in after-hours trading. The stock gained $40.36, or 22%, to $227.99 in after-hours action. In the regular session shares rose 8.8%.
In a separate Phase 2 trial in South Africa, the vaccine candidate showed 55.4% efficacy against the variant spreading there in HIV-negative trial participants. It also provided 100% protection against severe disease and hospitalization, the company said.
Novavax said the data would be used in applications for regulatory approval of the vaccine candidate worldwide.
A separate trial of the vaccine candidate is currently underway in the U.S. and Mexico. That trial began in December 2020.
To date, three vaccines against COVID-19 have been given emergency use authorization in the U.S. They include one jointly developed by Pfizer (PFE) - Get Report and BioNTech (BNTX) - Get Report, a second by Moderna (MRNA) - Get Report and a third by Johnson & Johnson (JNJ) - Get Report. The Johnson & Johnson vaccine requires only a single shot, while the others, including Novavax's, require follow up booster shots a few weeks after the initial inoculation.
Thursday afternoon, administration officials said President Biden will ask states to make all adults in the U.S. eligible for COVID-19 vaccines by May 1, and set a goal for the public to be able to gather in small groups during the July 4th holiday, according to a report in the Wall Street Journal.