Jab rollout halted over variant

South Africa halted the rollout of AstraZeneca's Covid-19 vaccinations after data showed it gave minimal protection against mild infection from one variant, stoking fears of a much longer battle with the pathogen.

The coronavirus has killed 2.3 million people, and variants have raised fears vaccines will need to be tweaked and people given booster shots.

Researchers from the University of Witwatersrand and the University of Oxford said the AstraZeneca vaccine provided minimal protection against mild or moderate infection from the South African variant among young people.

"This study confirms the pandemic coronavirus will find ways to continue to spread in vaccinated populations," said Andrew Pollard, chief investigator on the Oxford vaccine trial.

"But taken with the promising results from other studies in South Africa ... vaccines may continue to ease the toll on health care systems by preventing severe disease."

The AstraZeneca vaccine was the big hope for Africa as it is easier to store and transport than others. This makes South Africa's move a major blow, with implications for other regions.

An analysis of infections by the South African variant showed only a 22-percent lower risk of developing mild-to-moderate Covid-19 versus those given a placebo. If vaccines do not work as effectively as hoped against variants, the world could be facing a much longer battle.

While the lead investigator on the trial said data indicated protection against severe disease was likely from the vaccine, the study raised the prospect of repeated vaccination against a changing virus.

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 percent, suggested it would still prevent serious illness or death.

Sarah Gilbert, a professor of vaccinology at the University of Oxford, said efforts were under way to develop booster shot vaccines that will protect against variants.