On Nov. 23, 2020, AstraZeneca announced positive high-level results from an interim analysis of clinical trials of AZD1222 in the UK and Brazil showed the vaccine was highly effective in preventing COVID-19, the primary endpoint, and no hospitalisations or severe cases of the disease were reported in participants receiving the vaccine.

There were a total of 131 COVID-19 cases in the interim analysis. The combined analysis from both dosing regimens (n=11,636) resulted in an average efficacy of 70%.