British-Swedish pharmaceutical major AstraZeneca on Monday said its vaccine demonstrated the efficacy of 79 per cent at preventing symptomatic Covid-19 and 100 per cent efficacy at preventing severe disease and hospitalisation in a phase-3 trial in the US.
The results come after several countries in Europe briefly suspended the use of the AstraZeneca Covid-19 vaccine over fears of harmful side effects.
In the US trial, the vaccine was well-tolerated, and the independent data safety monitoring board (DSMB) identified no safety concerns related to the vaccine, AstraZeneca said.
The DSMB conducted a specific review of thrombotic events, as well as cerebral venous sinus thrombosis (CVST) - which refers to presence of a blood clot in the dural venous sinuses - with the assistance of an independent neurologist.
The board found no increased risk of thrombosis or events characterised by thrombosis among the 21,583 participants receiving at least one dose of the vaccine.
The specific search for cerebral venous sinus thrombosis found no events in this trial, AstraZeneca said, adding that vaccine efficacy was consistent across ethnicity and age.
Notably, in participants aged 65 years and over, vaccine efficacy was 80 per cent, the company said.
"These findings reconfirm previous results observed in AZD1222 trials across all adult populations but it's exciting to see similar efficacy results in people over 65 for the first time," Ann Falsey, Professor of Medicine, University of Rochester School of Medicine, US, and co-lead Principal Investigator for the trial, said in a statement.
"This analysis validates the AstraZeneca Covid-19 vaccine as a much-needed additional vaccination option, offering confidence that adults of all ages can benefit from protection against the virus."
Several countries in Europe including Germany and France last week lifted suspension on the use of the AstraZeneca Covid-19 vaccine amid a renewed surge in cases.
AstraZeneca said it will continue to analyse the data from the US trial and prepare for the primary analysis to be submitted to the US Food and Drug Administration (FDA) for Emergency Use Authorisation in the coming weeks.