A US government agency Tuesday raised concerns that AstraZeneca may have included out-of-date drug data in information provided during US trials for its Covid-19 vaccine.

A monitoring board had "expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data," a statement from the National Institute of Allergy and Infectious Diseases said.

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

The statement comes after AstraZeneca said Monday that stage three US trials had showed its Covid-19 vaccine was 79 percent effective at preventing the disease.

AstraZeneca said it was preparing to submit its findings to the US Food and Drug Administration to authorize the shot for emergency use.

The AstraZeneca vaccine is cheaper and easier to store than many of its rivals, but several countries in Europe and other parts of the world last week suspended its use because of isolated cases of blood clots.