The US National Institute of Allergy and Infectious Diseases (NIAID) was notified by the independent monitoring board that it was "concerned by information released by AstraZeneca on initial data from its COVID-19 vaccine clinical trial".
Speaking on Tuesday, the NIAID said, "The DSMB (the safety monitoring board) expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data."
Responding, AstraZeneca stated that the published results were based on "pre-specified interim analysis" of data up to February 17.
"We have reviewed the preliminary assessment of the primary analysis and the results were consistent with the interim analysis", it said. "We will immediately engage with the independent data safety monitoring board (DSMB) to share our primary analysis with the most up-to-date efficacy data.
"We intend to issue results of the primary analysis within 48 hours."
The trial showed that the AstraZeneca vaccine was 79 percent effective at stopping symptomatic COVID-19 and 100 percent effective at preventing people from falling seriously ill.
It also revealed that there were no major issues relating to blood clots - something that has been of major concern to some regulators in Europe.