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Latest AstraZeneca Report Supports Effectiveness Of COVID Vaccine

A patient gets the AstraZeneca vaccine on Wednesday in London.
Dan Kitwood
Getty Images
A patient gets the AstraZeneca vaccine on Wednesday in London.

Updated study results say the vaccine is 76% effective against symptomatic COVID-19 and 100% effective against severe disease. Independent monitors had been concerned about a previous report.

Updated March 24, 2021 at 11:03 PM ET

AstraZeneca's latest data analysis affirms effectiveness of its COVID-19 vaccine and is roughly in line with the results released Monday.

The latest analysis finds the vaccine to be 76% effective against symptomatic COVID-19 and 100% effective against severe or critical disease and hospitalization. These results are very close to the results that came out at the beginning of the week: 79% vaccine efficacy at preventing symptomatic COVID-19 and 100% effective against severe or critical disease and hospitalization.

An independent monitoring board raised questions about the company's release Monday — a day after the company announced that the higher efficacy rate-- saying it didn't include more up-to-date cases that were available.

Other scientists, including White House COVID adviser Dr. Anthony Fauci, said the company knew that 79% figure might be an overstatement because it was based on outdated data.

"This is really what you call an unforced error because the fact is this is very likely a very good vaccine," Fauci said, speaking on Tuesday on Good Morning America.

The Data and Safety Monitoring Board called on AstraZeneca to recalculate their numbers using information based on where the company's trial stood in March when there were more COVID cases included in the study, rather than the earlier report based on February's statistics.

The updated analysis includes 49 more cases of COVID-19 than the Monday analysis, which drew down the efficacy rates of the vaccine by 3%.

The latest analysis doesn't include details on side effects or adverse events. AstraZeneca said only that it didn't identify any safety concerns related to the vaccine.

Rare reports of blood clots after vaccination led some countries to suspend use of the vaccine. The European Medicines Agency investigated the adverse events and concluded last week that the benefits of the vaccine outweighed its risks. That determination led most countries that had put a pause on the vaccine to resume immunizations with it.

It's possible that the efficacy results reported Wednesday for the vaccine could still change some. The latest analysis is based on 190 cases of COVID-19 among the more than 32,000 volunteers in the study. Fourteen more cases of possible or probable COVID-19 still need to adjudicated and factored into the analysis.

AstraZeneca said it would submit the results to a peer-reviewed journal within weeks.

But the ultimate arbiter of the AstraZeneca data will be the U.S. Food and Drug Administration. The company said it is preparing to submit its package of data to the agency in support of an application for emergency use authorization of the vaccine during the pandemic.

After the FDA reviews the submission, a committee of expert advisers to the agency would meet in public and vote on whether the agency should move ahead with an authorization.

Copyright 2021 NPR. To see more, visit

Scott Hensley edits stories about health, biomedical research and pharmaceuticals for NPR's Science desk. During the COVID-19 pandemic, he has led the desk's reporting on the development of vaccines against the coronavirus.
Vanessa Romo is a reporter for NPR's News Desk. She covers breaking news on a wide range of topics, weighing in daily on everything from immigration and the treatment of migrant children, to a war-crimes trial where a witness claimed he was the actual killer, to an alleged sex cult. She has also covered the occasional cat-clinging-to-the-hood-of-a-car story.