New AstraZeneca COVID-19 Vaccine Data Show 100% Efficacy Against Severe Disease, 79% Against Symptomatic Disease


The independent data safety monitoring board conducted a specific review of thrombotic events related to AstraZeneca’s COVID-19 vaccine and found no increased risk.

New data from AstraZeneca have shown 79% efficacy against symptomatic COVID-19 disease, as well as 100% efficacy against severe or critical disease and hospitalization, according to a press release.

The interim safety and efficacy analysis was based on 32,449 participants, 141 of whom had symptomatic cases of COVID-19. The trial had a 2:1 randomization of vaccine to placebo, and efficacy was consistent across ethnicity and age. Notably, according to the press release, participants aged 65 years and older had vaccine efficacy of 80%.

“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 co-lead principal investigator Ann Falsey, MD, a professor of medicine at the University of Rochester School of Medicine, in a press release. “This analysis validates the AstraZeneca COVID-19 vaccine as a much-needed additional vaccination option, offering confidence that adults of all ages can benefit from protection against the virus.”

The AstraZeneca-led US phase 3 trial included 2 doses administered at a 4-week interval. Earlier trials have shown that an extended interval of up to 12 weeks demonstrated greater efficacy, which was also supported by immunogenicity data.

The vaccine was well tolerated, with no identified safety concerns related to the vaccine, according to AstraZeneca. The independent data safety monitoring board conducted a specific review of thrombotic events, as well as cerebral venous sinus thrombosis (CVST), and found no increased risk of thrombosis or events characterized by thrombosis among the 21,583 participants who received at least 1 dose. The specific search for CVST found no events in this clinical trial.

Officials with AstraZeneca will continue to analyze the data and prepare for the primary analysis to be submitted to the FDA for Emergency Use Authorization in the coming weeks, according to the press release. At the same time, the primary analysis will also be submitted to a peer-reviewed journal.

Among participants in the interim analysis, approximately 79% were Caucasian, 8% were Black, 4% were Native American, 4% were Asian, and 22% were Hispanic. Approximately 20% were 65 years of age or older and approximately 60% had comorbidities associated with an increased risk for severe COVID-19, such as diabetes, severe obesity, or cardiac disease.

“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, PhD, executive vice president of BioPharmaceuticals Research & Development at AstraZeneca, in the press release. “We are confident this vaccine can play an important role in protecting millions of people worldwide against this lethal virus. We are preparing to submit these findings to the US Food and Drug Administration and for the rollout of millions of doses across America should the vaccine be granted US emergency use authorization.”


AZD1222 US Phase III trial met primary efficacy endpoint in preventing COVID-19 at interim analysis [news release]. AstraZeneca; March 22, 2021. Accessed March 22, 2021.

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