AstraZeneca's COVID-19 vaccine provides minimal protection against South African strain

Data from a small clinical trial in South Africa has found that AstraZeneca's AZD1222 vaccine provides minimal protection against mild and moderate illness from COVID-19 caused by the country's B.1.351 variant.

South Africa's health minister Zweli Mkhize said on Sunday the country, which had planned to administer a first shipment of 1 million doses of the vaccine to healthcare workers later this month, would temporarily halt the rollout of the vaccine. Mkhize said the country would now wait for more information on the vaccine's efficacy.

10% efficacy rate

The trial, submitted as a pre-print prior to peer-review publication, enrolled around 2000 participants with a median age of 31 years. Of the 39 participants that were found to be infected with the B.1.351 variant, 19 had received the vaccine, while 20 had received a placebo, said principal investigator Shabir Madhi. While those numbers imply an around 10% efficacy rate protecting against mild and moderate COVID-19 from the new variant, Madhi added that the data were too limited to be statistically significant.

Still, Andrew Pollard, director of the Oxford Vaccine Group at the University of Oxford, which developed the vaccine with AstraZeneca, noted that "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." As with other drugmakers, AstraZeneca said it is working on updating its vaccines to target new variants of the virus, and hopes to have a new vaccine ready by the fall.

Pfizer and Moderna have both said that preliminary laboratory studies indicate that their vaccines are less effective against the B.1.351 variant. Johnson & Johnson and Novavax, whose vaccines have yet to be authorised in any country, have also found that their vaccines were less effective in recent clinical trials in South Africa, compared with trials in the US or the UK.

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