AstraZeneca may have provided an incomplete view of efficacy data on its COVID-19 vaccine from a large scale US trial, says the country’s National Institute of Allergy and Infectious Diseases (NIAID), in a fresh setback to the vaccine.

AstraZeneca said on Monday its COVID-19 vaccine developed with Oxford University in the UK was 79% effective in preventing symptomatic illness in a large trial in the US, Chile and Peru.

However, on Tuesday the NIAID said the independent Data Safety Monitoring Board (DSMB) had expressed some concerns about the trial data.

“The DSMB expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data.”