Pfizer and BioNTech said that clinical trial data suggested their Covid-19 jab could be effective against the more contagious B.1.351 mutation, which was initially detected in South Africa.The vaccine showed 100 per cent efficacy in South Africa, where B.1351 was prevalent, the companies said. Only 800 participants were enrolled in the country, however, meaning that the latest findings are still limited.

The study said nine people in South Africa went down with Covid-19, all of whom were in the placebo group. None who had taken the companies’ vaccine were infected. Lab analysis of nine of the infections showed that six of the nine were from the B.1.351 strain.

“These data also provide the first clinical results that a vaccine can effectively protect against currently circulating variants, a critical factor to reach herd immunity and end this pandemic for the global population,” said Ugur Sahin, chief executive and co-founder of BioNTech.

Analysis of the trial of 46,306 people also showed strong protection in 12,000 vaccinated participants who had received their second dose at least six months earlier, with an efficacy rate of 91 per cent.

Overall trial data showed protection in 91 per cent of cases, slightly lower than the original 95 per cent efficacy rate reported previously. Since those earlier trials, several variants of the coronavirus have appeared.Health experts are particularly concerned about B.1.351 and the P.1 variant, which was first identified in travellers from Brazil. Pfizer and BioNTech have also begun testing the efficacy of their vaccine against P.1 but have yet to release their findings.The new trial data could help the companies begin to push for regulatory approval in the US, beyond the emergency authorisation the vaccine has already received. The findings “confirm the favourable efficacy and safety profile of our vaccine”, Albert Bourla, Pfizer chief executive, said in a statement.