AstraZeneca’s investigational vaccine candidate AZD1222 was found to be highly effective in preventing coronavirus disease 2019 (COVID-19), with an average efficacy rate of 70% based on the combined interim analysis of 2 trials.

AZD1222 utilizes a replication-deficient chimpanzee adenovirus to deliver a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) protein to induce a protective immune response. The ongoing trials (COV002 and COV003) are evaluating the efficacy, safety and immunogenicity of AZD1222 in over 23,000 participants aged 18 years or older, who are healthy or have medically stable chronic diseases and are at increased risk of exposure to SARS-CoV-2 virus. Participants were randomized to receive 2 intramuscular doses of either a half-dose/full-dose regimen or a full-dose regimen of AZD1222 given at least 1 month apart or a comparator, meningococcal conjugate vaccine (MenACWY) or saline.

Pooled analyses of the trials showed that AZD1222 met the primary end point with a vaccine efficacy of 90% and 62% in participants treated with the half-dose/full-dose and full-dose regimens, respectively (P ≤.0001). The combined analysis of both dosing regimens (n=11,636) demonstrated an average vaccine efficacy of 70% (P ≤.0001).

A total of 131 cases of COVID-19 were reported in the interim analysis, with no hospitalizations or severe cases noted in participants who received the vaccine. Additionally, both dosing regimens were observed to be well tolerated with no serious adverse events reported. 

Based on these findings, AstraZeneca will seek an Emergency Use Listing from the World Health Organization (WHO) for an accelerated pathway to vaccine availability in low-income countries. Pending regulatory approval, the Company intends to supply up to 3 billion doses of the vaccine, which can be stored and transported at normal refrigerated conditions, in 2021. 

For more information visit or


AZD1222 vaccine met primary efficacy endpoint in preventing COVID-19. [press release]. Wilmington, DE: AstraZeneca; November 23, 2020.