AstraZeneca said on Thursday its COVID-19 vaccine was 76% effective at preventing symptomatic illness, citing a new analysis of up-to-date results for its major US trial. US health officials earlier in the week publicly rebuked the drugmaker for using "outdated information" when calculating that the vaccine was 79% effective.
That marked a new setback for the vaccine that was once hailed as a milestone in the fight against the COVID-19 pandemic, but has been dogged by questions over its effectiveness and possible side-effects. AstraZeneca reiterated on Thursday that the shot, developed with Oxford University, was 100% effective against severe or critical forms of the disease.
It also said the vaccine showed 86% efficacy in adults 65 years and older. The latest trial data, which has yet to be reviewed by independent researchers or regulators, was based on 190 infections and 32,449 participants in the United States, Chile and Peru. The earlier interim data was based on 141 infections through Feb. 17.
The updated 76% efficacy rate compares with rates of about 95% for vaccines from Pfizer/BioNTech and Moderna. The AstraZeneca vaccine is, however, seen as crucial in tackling the spread of COVID-19 across the globe, not just due to limited vaccine supply but also because it is easier and cheaper to transport than rival shots. It has been granted conditional marketing or emergency use authorization in more than 70 countries.
The shot has faced questions since late last year when the drugmaker and Oxford University published data from an earlier trial with two different efficacy readings as a result of a dosing error. Then this month, more than a dozen countries temporarily suspended giving out the vaccine after reports linked it to a rare blood clotting disorder in a very small number of people.
The European Union's drug regulator said last week the vaccine was clearly safe, but Europeans remain sceptical about its safety.