Kate Bingham, Chair of the Government's Vaccine Taskforce, after starting her Novavax trial at the Royal Free Hospital, north London on October 13, 2020.
Kirsty O'Connor/PA Images via Getty Images
  • Novavax on Thursday said that its vaccine was 89% effective at preventing cases of Covid-19, based on results from a UK trial.
  • In a trial in South Africa, the vaccine was far less effective, possible because of a coronavirus variant that has emerged there.
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Novavax on Thursday said its experimental coronavirus vaccine was highly effective at preventing the disease in a UK trial, but disappointing results from a study of the same shot in South Africa raise questions.

The vaccine developer said that its shot was 89% effective at preventing symptomatic Covid-19, based on a trial of more than 15,000 patients taking place in the UK. The company published the results in a press release, and said it plans to submit them to a scientific journal for review. 

But results from a smaller trial in South Africa, the results weren't quite as promising. The vaccine was only 49% effective at preventing symptomatic cases of COVID-19 in that 4,400-participant study. Among people who are HIV negative, it was 60% effective. 

The trial, which took place from August through mid-January, occurred as a new variant emerged in South Africa that is more infectious. 

“The higher efficacy of the vaccine in the UK than in South Africa is because the variants circulating in SA are less sensitive to vaccine induced immune responses," says Professor Shabir Madhi, Executive Director of the Vaccines and Infectious Diseases Analytics Research Unit (VIDA) at Wits, and principal investigator in the Novavax Covid-19 vaccine trial in South Africa.

"Nevertheless, the 60% reduced risk against Covid-19 illness in vaccinated individuals in South Africans underscores the value of this vaccine to prevent illness from the highly worrisome variant currently circulating in South Africa, and which is spreading globally. This is the only Covid-19 vaccine for which we now have objective evidence that it protects against the variant dominating in South Africa.”

Some preliminary research has raised concerns that current coronavirus vaccines may not work as well against that variant, though both Moderna and Pfizer have said they expect that their shots will still work. 

The variant, B.1.351, was discovered in December and has spread to 30 countries. 

Novavax is still signing up patients for a larger test of its vaccine in the US and Mexico. The company said it expects to finish enrolling volunteers in that 30,000-person trial by the middle of February.

It's not clear whether US regulators would require results from the US trial before making a decision on whether to allow the vaccine to be given more widely. Novavax said it's already shared information on its vaccine with the UK pharmaceutical regulator.

Additional reporting by Business Insider SA team.

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