The drug maker said on Monday that trials in Chile, Peru and the U.S. found the vaccine, developed in conjunction with Oxford University, was 79 per cent effective in preventing symptomatic COVID-19 and crucially, posed no increased risk of blood clots.
It intends to request U.S. emergency authorisation in coming weeks.
More than a dozen European countries, including Germany and France, had halted use of the AstraZeneca vaccine earlier this month after some reports linked it to blood clots in a very small number of people.
They have since resumed inoculation after a regional regulator said it was safe but an opinion poll showed Europeans remained sceptical over its safety.
Hailed as a milestone in the fight against the COVID-19 pandemic when it first emerged as a vaccine contender last year, the AstraZeneca shot has since been dogged by confusion over its efficacy dosing regimen.
Its possible side-effects as well as supply setbacks in Europe, where the company has been at the centre of a growing conflict between Brussels and London over so-called vaccine nationalism.
The latest data should help address some of those concerns, analysts said.
Based on more than 32,000 people, the trial was larger and elderly volunteers featured more prominently than in previous trial results from the UK which had prompted some European countries to initially hold back using the AstraZeneca shot on older people.
It is clear this vaccine has very good efficacy (remember that 60 per cent was, prior to any trials regarded as good target), and that this efficacy does not show a notable decline at older ages, said Stephen Evans, Professor of Pharmacoepidemiology at the London School of Hygiene