Results from the trial, which included more than 300,000 people, found that the jab is 79 per cent effective against preventing symptomatic Covid-19 and 100 per cent effective against severe disease and hospitalisation.
The trial, which took place across 88 centres in the US, Peru and Chile, was meant to address any concerns felt by the US, which is yet to approve the jab.
But the Data and Safety Monitoring Board, which oversees clinical trials, notified the National Institute of Allergy and Infectious Diseases (NIAID) that “it was concerned by information released by AstraZeneca,” the NIAID said in a statement.
NIAID said it then urged the AstraZeneca firm to work with the monitoring board “to review the efficacy data and ensure the most accurate, up-to-date efficacy data be made public as quickly as possible.”
Over the last few days, the monitoring board’s analysis of the vaccine trial was delayed several times because it had to ask for revised reports from those handling trial data on behalf of the firm, according to a person familiar with the matter, who the New York Times said was not authorised to discuss the issue publicly.
In a statement, AstraZeneca has said it will continue to analyse the data and prepare for the primary analysis to be submitted to the US Food and Drug Administration for emergency use authorisation in the coming weeks.
But Monday’s results from the independent trial stated that no increased risk of blood clots were found.
A similar verdict was previously confirmed by the European Union’s Medicines regulator who said it remains “firmly convinced” that the benefits of the jab outweigh the risks.