Astra shot may stop severe disease with SA variant

"The key thing is there doesn't appear to be any evidence that it's any less effective at preventing severe disease.

"What we're less sure about is how effective it is against mild and moderate disease, and that means that people who have the vaccine could potentially still be infected and still pass the virus on if they get infected with this South African variant," said Tildesley, of University of Warwick and who also advises the government.

South Africa halted Monday's planned 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 cat-and-mouse battle with the pathogen.

The coronavirus has killed 2.3 million people and turned normal life upside down for billions but new variants have raised fears that vaccines will need to be tweaked and people may have to have booster shots.

Britain has urged calm, citing evidence that the vaccines prevented grave illness and death, while AstraZeneca said it believed its vaccine could protect against severe disease.