Pfizer Inc and BioNTech’s COVID-19 vaccine appeared to work against a key mutation in the highly transmissible new variants of the coronavirus discovered in the UK and South Africa, according to a laboratory study conducted by the U.S. drugmaker, Reuters reports.

The not-yet peer reviewed study by Pfizer and scientists from the University of Texas Medical Branch indicated the vaccine was effective in neutralizing virus with the so-called N501Y mutation of the spike protein.

The mutation could be responsible for greater transmissibility and there had been concern it could also make the virus escape antibody neutralization elicited by the vaccine, said Phil Dormitzer, one of Pfizer’s top viral vaccine scientists.

The study was conducted on blood taken from people who had been given the vaccine. Its findings are limited, because it does not look at the full set of mutations found in either of the new variants of the rapidly spreading virus.