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Primary analysis results confirm AstraZeneca-Oxford COVID-19 vaccine efficacy

Roshini Claire Anthony
05 Apr 2021

Primary analysis of the D8110C00001 trial showed that the COVID-19 vaccine AZD1222 had 76 percent efficacy at preventing symptomatic COVID-19.

“The primary analysis is consistent with our previously released interim analysis and confirms that our COVID-19 vaccine is highly effective in adults, including those aged 65 years and over,” said Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, AstraZeneca. [https://www.astrazeneca.com/media-centre/press-releases/2021/azd1222-us-phase-iii-primary-analysis-confirms-safety-and-efficacy.html, accessed 31 March 2021]

Participants in this phase III, double-blind trial were 32,449 individuals aged 18 years who were healthy or with medically stable chronic diseases and were enrolled at 88 trial sites in the US, Peru, and Chile. They were randomized 2:1 to receive two intramuscular injections of the AZD1222 vaccine or placebo, with 4 weeks between doses. [https://www.niaid.nih.gov/news-events/phase-3-clinical-testing-us-astrazeneca-covid-19-vaccine-candidate-begins, https://www.astrazeneca.com/media-centre/press-releases/2021/azd1222-us-phase-iii-primary-analysis-confirms-safety-and-efficacy.html, accessed 31 March 2021]

The primary analysis included the accrual of 190 individuals with symptomatic COVID-19, 49 more than that of the interim analysis. The statistical plan required 75 and 150 adjudicated cases for the interim and primary analyses, respectively.

The results showed that, 15 days following two doses of the vaccine, efficacy of the vaccine in preventing symptomatic COVID-19 was 76 percent (confidence interval, 68–82 percent). The vaccine had an efficacy of 85 percent (confidence interval, 58–95 percent) in individuals aged 65 years. Overall, efficacy results were comparable across age groups.

There was also 100 percent efficacy with regard to the key secondary endpoint of prevention of severe or critical disease or hospitalization. Eight cases of severe COVID-19 occurred, all in the placebo group.

The vaccine was well tolerated and there were no reports of vaccine-related safety concerns.

Fourteen possible or probable cases are yet to be adjudicated, which could potentially lead to minor alterations in the point estimate and number of cases.

The results show that the efficacy of the vaccine is consistent with that of the prespecified interim analysis which were released on 22 March 2021. These prespecified primary analysis results form the basis for regulatory submission for Emergency Use Authorization to the US Food and Drug Administration (FDA). This is in addition to the conditional marketing authorization or emergency use authorization that has been granted in >70 countries.

Follow-up for this trial is ongoing and participants will continue to be followed up for 2 years after their second injection.

The primary analysis results have been submitted to the independent Data Safety Monitoring Board and will also be submitted for peer-reviewed publication.

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01 Apr 2021
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