South Africa halted the rollout of AstraZeneca's COVID-19 vaccinations after data showed it gave minimal protection against mild infection from one variant, but Britain said the shot still stopped death and serious illness.
The novel coronavirus has killed 2.3 million people and turned normal life upside down for billions but new variants of the virus have raised fears that the world could be locked in a cat-and-mouse battle for years with the pathogen.
Researchers from the University of Witwatersrand and the University of Oxford said in a prior-to-peer analysis that the AstraZeneca vaccine provided minimal protection against mild or moderate infection from the so-called South African variant among young people.
Professor Shabir Madhi, lead investigator on the AstraZeneca trial in South Africa, said the vaccine's similarity to another produced by Johnson & Johnson, which reduced severe disease by 89%, suggested it would still prevent serious illness or death.
"There's still some hope that the AstraZeneca vaccine might well perform as well as the Johnson & Johnson vaccine in a different age group demographic that I address of severe disease," he told BBC radio.
Andrew Pollard, chief investigator on the Oxford vaccine trial, said the South African study had shown that the virus would, as expected, find ways to continue to spread in vaccinated populations.
"But, taken with the promising results from other studies in South Africa using a similar viral vector, vaccines may continue to ease the toll on health care systems by preventing severe disease," Pollard said.
While thousands of individual changes have arisen as the virus mutates on replication and evolves into new variants, only a tiny minority are likely to be important or change the virus in an appreciable way, according to the British Medical Journal.