New York, Mar 25 (IANS): British-Swedish drugmaker AstraZeneca on Thursday said that its Covid-19 vaccine's efficacy at preventing symptomatic coronavirus was 76 per cent in a US phase-3 trial, slightly lower than 79 per cent efficacy that it projected earlier this week.

The revised efficacy estimate came after an independent board said that the 79 per cent efficacy results of the vaccine might have been based on outdated information.

This new efficacy analysis included the accrual of 190 symptomatic cases of Covid-19 from the 32,449 trial participants, an additional 49 cases to the previously announced interim analysis, AstraZeneca said.

Participants were randomised on a 2:1 ratio between the vaccine and placebo group.

The results showed that vaccine efficacy at preventing symptomatic Covid-19 was 76 per cent occurring 15 days or more after receiving two doses given four weeks apart.

In addition, results were comparable across age groups, with vaccine efficacy of 85 per cent in adults 65 years and older.

A key secondary endpoint, preventing severe or critical disease and hospitalisation, demonstrated 100 per cent efficacy, the company said.

There were eight cases of severe Covid-19 observed in the primary analysis with all of those cases in the placebo group.

The vaccine was well tolerated, and no safety concerns related to the vaccine were identified, according to the data.

"The primary analysis is consistent with our previously released interim analysis, and confirms that our Covid-19 vaccine is highly effective in adults, including those aged 65 years and over," Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D at AstraZeneca, said in a statement.

"We look forward to filing our regulatory submission for Emergency Use Authorisation in the US and preparing for the rollout of millions of doses across America."

AstraZeneca said it will also submit the primary analysis for peer-reviewed publication in the coming weeks.