AstraZeneca Reports COVID-19 Vaccine Met Primary Efficacy End Point


One vaccine dosing regimen for AZD1222 showed 90% efficacy, according to investigators at the University of Oxford.

AstraZeneca's COVID-19 vaccine candidate

Results of an interim analysis for AstraZeneca’s coronavirus disease 2019 (COVID-19) vaccine, AZD1222, demonstrated that the vaccine candidate met the primary efficacy end point of preventing COVID-19 infection.

The United Kingdom-based study evaluated 2 dosing regimens. The first, in which the vaccine is administered as a half dose followed by a full dose at least 1 month later, showed 90% efficacy; the other regimen – 2 full doses at least 1 month apart – demonstrated 62% efficacy. Overall, investigators reported an average vaccine efficacy of 70%, with all results deemed statistically significant.

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The analysis, which included data from the COV002 phase 2/3 trial in the UK as well as the COV003 phase 3 trial in Brazil, also reported no hospitalizations or severe cases of COVID-19. Both COV002 and COV003 are single-blinded, multicenter, randomized controlled trials (RCTs) assessing the safety, efficacy, and immunogenicity of AZD1222.

More than 23,000 participants are being assessed in the 2 clinical trials; with studies also taking place in the US, Japan, Russia, South Africa, Kenya, and Latin America. Investigators expect to enroll up to 60,000 participants worldwide.

The vaccine candidate was co-created by the University of Oxford and Vaccitech through the use of a replication-deficient chimpanzee viral vector based on a weakened version of adenovirus, a common cold virus that contains the genetic material of the SARS-CoV-2 virus spike protein.

As a result of the findings, AstraZeneca intends to submit AZD1222 to receive Emergency Use Listing status from the World Health Organization (WHO). The designation would facilitate COVID-19 vaccine availability and uptake in low-income countries, according to the news release.

“These findings show that we have an effective vaccine that will save many lives,” said Andrew Pollard, BSc MBBS PhD, chief investigator of the study. “Excitingly, we’ve found that one of our dosing regimens may be around 90% effective and if this dosing regimen is used, more people could be vaccinated with planned vaccine supply,” he continued.

Additionally, local and systemic reactions to AstraZeneca’s COVID-19 vaccine were less common in older adults (56 years and older) than younger adults, according to AstraZenca’s phase 2/3 trial results, published in The Lancet.2

In those receiving 2 standard doses of the vaccine, after the prime vaccination, local reactions were reported in 88% of those in the 18 to 55 years old group, 73% in the 56 to 69 years group, and 61% in the 70 years and older group.

Although the vaccine appears to be better tolerated in older adults than in younger adults, it had similar immunogenicity across all age groups after a boost dose, the researchers said. “Further assessment of the efficacy of this vaccine is warranted in all age groups and individuals with comorbidities,” they added.


  1. AZD1222 vaccine met primary efficacy endpoint in preventing COVID-19. News Release. AstraZeneca; November 23, 2020. Accessed November 23, 2020.

2. Ramasamy, M., Minassian, A., et al. Safety and immunogenicity of ChAdOx1 nCoV-19 vaccine administered in a prime-boost regimen in young and old adults (COV002): a single-blind, randomised, controlled, phase 2/3 trial. The Lancet. November 18, 2020.

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