Part of the trial took place in South Africa, where a variant first emerged — known as B.1.351 — which some scientists worry might be able to escape existing vaccines.

There have been 312 identified cases of this strain in the United States, according to the latest figures from the CDC.

In the Pfizer-BioNTech trial, six cases of this variant were observed, but none of them were people who had been given the vaccine — indicating an efficacy of 100 percent, it said.

This was welcomed by the drugmakers, because in February they said a laboratory test suggested that their vaccine produced lower levels of antibodies against this strain.

Although the antibody levels were lower, “it does not appear to affect the high observed efficacy against this variant,” the statement said Thursday.