AstraZeneca Plc's Covid-19 vaccine demonstrated 74% efficacy at preventing symptomatic disease, a figure that increased to 83.5% in people aged 65 and older, according to long-awaited results of the company's US clinical trial published on Wednesday.
Overall efficacy of 74% was lower than the interim 79% figure reported by the British drugmaker in March, a result AstraZeneca revised days later to 76% after a rare public rebuke from health officials that the figure was based on "outdated information."
The data looked at more than 26,000 volunteers in the United States, Chile and Peru, who received two doses of the vaccine spaced about a month apart. The results were published in the New England Journal of Medicine.
There were no cases of severe or critical symptomatic Covid-19 among the more than 17,600 participants who got the vaccine, compared with 8 such cases among the 8,500 volunteers who got the placebo. There were also two deaths in the placebo group but none among those who received the vaccine.