Astra shot doesn’t thwart South Africa variant, show study data × Vaccine had only 10% efficacy against the variant strain; however, there were no instances of severe disease in either the group that received two shots of the vaccine or the one that got dummy shots AstraZeneca Plc’s embattled coronavirus vaccine didn’t offer much protection against mild disease caused by the variant that emerged in South Africa in a study that prompted the country to seek other immunisations last month. The vaccine had an efficacy of just 10 per cent against the variant strain, according to the study published on Tuesday in the New England Journal of Medicine. There were no instances of severe disease in either the group that received two injections of the vaccine or the one that got dummy shots.