British Transport Secretary Grant Shapps said on Friday there were concerns that Covid-19 vaccines might not work properly against the highly transmissible variant of the coronavirus discovered in South Africa.

The world’s leading Covid-19 vaccine makers are rushing to see if their shots work against new mutations of the novel coronavirus found in South Africa and the United Kingdom.

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. drug maker.

“The South African variant is worrying the experts because it may be that the vaccine doesn’t respond in the same way or doesn’t work in quite the same way,” Shapps told LBC radio. “This South African variant – this is a very big concern for the scientists.”

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.