AstraZeneca said on Thursday its Covid-19 vaccine was 76% effective at preventing symptomatic illness in 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 US health officials earlier in the week publicly rebuked the drugmaker for using "outdated information" for claiming that the vaccine was 79% effective. AstraZeneca on Thursday reiterated that the shot, developed with Oxford University, was 100% effective against severe or critical forms of the disease. It also said the vaccine showed 85% efficacy in adults 65 years and older.