Data from a US trial evaluating AstraZeneca’s COVID-19 vaccine, AZD1222, showed that it was 79% effective at preventing symptomatic COVID-19 disease.

AZD1222 utilizes a replication-deficient chimpanzee adenovirus to deliver a SARS-CoV-2 protein to induce a protective immune response. The phase 3, double-blind, placebo-controlled study [D8110C00001; NCT04516746] assessed the safety, efficacy, and immunogenicity of AZD1222 in 32,459 individuals 18 years of age or older; approximately 20% of the participants were 65 years or over and roughly 60% had comorbidities. Study participants were randomly assigned 2:1 to receive 2 intramuscular doses of AZD1222 or saline placebo 4 weeks apart.

Interim data demonstrated vaccine efficacy of 79% based on 141 symptomatic cases of COVID-19 among the 32,449 participants.  Vaccine efficacy was reported to be 80% in participants aged 65 years and over; comparable efficacy was also observed across ethnicity. The vaccine was also found to be 100% effective at preventing severe COVID-19 disease and hospitalization.

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“These findings reconfirm previous results observed in AZD1222 trials across all adult populations but it’s exciting to see similar efficacy results in people over 65 for the first time,” said Ann Falsey, Professor of Medicine, University of Rochester School of Medicine, US, and co-lead Principal Investigator for the trial.

As for safety, no issues were identified by the data safety monitoring board (DSMB), which also conducted a review of thrombotic events with the help of an independent neurologist. Among 21,583 participants who received at least 1 dose of the vaccine, the DSMB found no increased risk of thrombosis, as well as no reports of cerebral venous sinus thrombosis.

“These results add to the growing body of evidence that shows this vaccine is well tolerated and highly effective against all severities of COVID-19 and across all age groups,” said Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, AstraZeneca. “We are preparing to submit these findings to the FDA and for the rollout of millions of doses across America should the vaccine be granted emergency use authorization.”

The AstraZeneca COVID-19 vaccine can be stored at normal refrigerated temperatures for at least 6 months.


AZD1222 US phase III trial met primary efficacy endpoint in preventing COVID-19 at interim analysis. [press release]. Wilmington, DE: AstraZeneca; March 22, 2021.

This article originally appeared on MPR