Novavax's COVID-19 vaccine has been found to be almost 90 percent effective in a clinical trial in the United Kingdom, the company said Thursday, but was far less effective in a separate trial in South Africa given the variant prevalent there.
Efficacy was strong in the U.K. trial, at 89.3 percent, the company said. But in a separate, smaller trial in South Africa, where a more contagious variant of the virus has taken hold, efficacy fell sharply to 49.4 percent, though it was somewhat higher, at 60 percent, among participants who did not have HIV.
The results, therefore, have both positive and negative aspects, but the results on the South African variant add to the concern on that front.
The United States announced its first confirmed cases of the variant, in South Carolina, earlier on Thursday.
Both the Pfizer and Moderna vaccines have been found in early studies to produce a lower level of antibody response against the South African variant, but the companies said the response was still above the level considered effective.
Researchers have begun working on a booster shot specifically designed to fight the South African variant, if needed.
Novavax is still enrolling in its U.S. clinical trial, and it remains unclear when any Food and Drug Administration review of the vaccine would occur in the U.S.
Data from another vaccine, from Johnson & Johnson, are expected by early next week and are being closely watched to see if the U.S. can add a third vaccine to the rotation and to see if there is data on the performance against the South African variant.