South Africa has put its rollout of the Oxford-AstraZeneca vaccine on hold after a study showed “disappointing” results against its new Covid variant.
Scientists say the variant accounts for 90% of new Covid cases in South Africa.
The trial, involving some 2,000 people, found that the vaccine offered “minimal protection” against mild and moderate cases.
But experts are hopeful that the vaccine will still be effective at preventing severe cases.
South Africa has recorded almost 1.5 million coronavirus cases and more than 46,000 deaths since the pandemic began – a higher toll than any other country on the continent.
The country has received one million doses of the Oxford-AstraZeneca jab and was preparing to start vaccinating people.
The trial was carried out by researchers at the University of the Witwatersrand in South Africa and the UK’s Oxford University, but has not yet been peer reviewed.
The trial’s chief investigator, Prof Shabir Madhi, said it showed that “unfortunately, the AstraZeneca vaccine does not work against mild and moderate illness”.
Prof Madhi said the study had not been able to investigate the vaccine’s efficacy in preventing more serious infections, as participants had an average age of 31 and so did not represent the demographic most at risk of severe symptoms from the virus.
The vaccine’s similarity to one produced by Johnson & Johnson, which was found in a recent study to be highly effective at preventing severe disease in South Africa, suggested it would still prevent serious illness, according to Prof Madhi.
Other experts were also hopeful that the vaccine remained effective at combating more serious cases.