Biotech company Novavax announced Thursday that its coronavirus vaccine was more than 89% effective against Covid-19 in its Phase 3 clinical trial conducted in the UK.

The results were based on 62 confirmed Covid-19 infections among the 15,000 participants in the study. The company said 56 cases were seen in the placebo group, up from six cases in the group that received the vaccine. This resulted in an estimated vaccine effectiveness of 89.3%.

The company’s shares rose more than 23% in after-hours trading.

With the results, the company “has the potential to play an important role in solving this global public health crisis,” said Stanley Erck, CEO of Novavax, in a statement. “We look forward to continuing to work with our partners, employees, investigators and regulators around the world to make the vaccine available as soon as possible.”

The study also found that the vaccine against the British variant, also known as B.1.1.7, appeared to be 85.6% effective. A separate Phase 2 study in South Africa showed that the vaccine is nowhere near as effective against a new strain ravaging that country.

The shot was still considered effective in protecting against the virus, but with an effectiveness rate of only 49.4% among 44 Covid-19 cases in South Africa, where 90% of the cases contain the problematic new variant, the company said.

Due to the lower effectiveness against the strain in South Africa, Novavax plans to select a modified version of the vaccine to provide better protection against the new strain “in the coming days”. The modified vaccine is scheduled to be tested in the second quarter of this year.

Novavax is among several companies developing a vaccine against the virus which, according to Johns Hopkins University, infected more than 101 million people worldwide and killed at least 2.2 million people as of Thursday. To date, only two vaccines – from Pfizer and Moderna – have been approved for use in the United States.

In July, as part of the Trump administration’s Operation Warp Speed ‚Äč‚Äčinitiative, the U.S. government announced that it would pay Novavax $ 1.6 billion to develop and manufacture the potential vaccine, with a goal of 100 million doses by early 2021 submit.

It’s unclear whether Thursday’s data will be enough for Novavax to obtain an emergency clearance from the Food and Drug Administration that would allow distribution in the U.S. The company began a late test involving 30,000 people in the US and Mexico late December.

Novavax’s vaccine contains synthesized parts of the surface protein that the coronavirus uses to infect humans. The company said the vaccine was well tolerated, adding that “serious, serious and medically treated adverse events occurred in low levels and were balanced between vaccine and placebo groups”.

In August, the company announced that data from the first phase of the study showed that the vaccine had produced a promising immune response. Participants received two doses of the potential vaccine, approximately 21 days apart, by intramuscular injection. Novavax also said the vaccine was well tolerated and no serious adverse events were reported.