The company is preparing to seek emergency approval for use of the shot in the US.
AstraZeneca says its vaccine has 76% efficacy against symptomatic Covid-19, after the firm updated analysis of the third phase of testing.
The revised number follows figures released on Monday reporting the jab was 79% effective, which US federal health officials expressed concern were based on “outdated information”.
In its statement on Thursday the company said the latest analysis confirms “vaccine efficacy consistent with the pre-specified interim analysis” announced on Monday.
The firm said its vaccine also has 100% efficacy against severe or critical disease and hospitalisation due to coronavirus and is 85% effective against symptomatic Covid-19 in patients aged 65 years and over.
Analysis showed 190 symptomatic cases of the illness from the 32,449 trial participants, with the company saying that 76% efficacy was observed 15 days or more after two doses of its shot were given four weeks apart.