On Mar. 22, 2021, Oxford University announced that a Phase III study of the Oxford-AstraZeneca coronavirus vaccine conducted by AstraZeneca in the U.S., Chile and Peru had shown that vaccine is safe and highly effective, adding to previous trial data from the United Kingdom, Brazil and South Africa, as well as real-world impact data from the UK. These data show that the vaccine was 79% effective against symptomatic COVID-19, and 100% effective against severe, or critical symptomatic COVID-19.

These results also add to the extensive safety data collected both in previous trials and through real-world vaccine roll out schemes. The independent Data and Safety Monitoring Board (DSMB) reported no safety concerns among the participants receiving at least one dose of the vaccine.  

The absolute efficacy is higher in this new study than observed in the Oxford-led studies, as efficacy is affected by the protocol case definition (higher for more severe cases) and the population in which the study is conducted. Today’s findings are in line with findings from other major vaccine developers who studied efficacy in the US.