WASHINGTON (REUTERS) - British drugmaker AstraZeneca may have provided an incomplete view of efficacy data on its Covid-19 vaccine from a large-scale US trial, the US National Institute of Allergy and Infectious Diseases (NIAID) said on Tuesday (March 23).

AstraZeneca said a day earlier that its Covid-19 vaccine developed with Oxford University is 79 per cent effective in preventing symptomatic illness in a large trial in Chile, Peru and the United States.

"The DSMB expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data," the US agency said, referring to the independent Data Safety Monitoring Board (DSMB).

"We urge the company to work with the DSMB to review the efficacy data and ensure the most accurate, up-to-date efficacy data be made public as quickly as possible."

The United States phase three trial of the vaccine developed by AstraZeneca and Oxford University involved 32,449 participants, with two-thirds receiving the jab, the pharmaceutical firm said in a statement.

Around 20 per cent were 65 or older, and about 60 per cent had health conditions associated with a higher risk of severe Covid-19, such as diabetes, severe obesity or cardiac disease.

Some leading European Union countries have resumed AstraZeneca vaccinations after the European Medicines Agency said last Thursday that the jab is "safe and effective" and is not linked to an increased risk of blood clots.