US pharmaceutical firm Pfizer and its German partner BioNTech say their COVID-19 vaccine is more than 91 percent effective for up to six months after the second dose.
The firms on Thursday released the results of a clinical trial they conducted after their vaccine secured authorization for emergency use from the US Food and Drug Administration last December.
The updated data from a trial of more than 46,000 participants through March 13 showed 927 confirmed symptomatic cases of COVID-19.
The firms said that of these cases, 850 occurred among participants who got the placebo, while 77 were in the vaccinated group.
They said that corresponded to an efficacy rate of 91.3 percent in preventing symptomatic cases "measured seven days through up to six months after the second dose."
The companies said the results contained data on more than 12,000 participants who had been fully inoculated for at least six months.
They also released the results of a trial of 800 participants in South Africa, where a new variant of the coronavirus is circulating. They said there were nine cases of COVID-19, all of which were observed in the placebo group. Six of the nine cases were confirmed to be of the South African variant. The firms said the data demonstrates the vaccine's high efficacy against this variant.
Pfizer and BioNTech say they plan to share the results with worldwide regulatory agencies soon.