Updated Data Reveals AstraZeneca’s Vaccine Has Slightly Lower Efficacy Rate Than Initially Reported

Illustration for article titled Updated Data Reveals AstraZeneca’s Vaccine Has Slightly Lower Efficacy Rate Than Initially Reported
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AstraZeneca’s attempt to receive federal approval for its coronavirus vaccine has been nothing short of a saga, and unfortunately it’s a saga that has only increased skepticism about the company’s vaccine. After being asked by health officials to provide updated data regarding the vaccine’s effectiveness, new data reveals the vaccine is slightly less effective than initially reported.


According to Politico, the British pharmaceutical company initially announced in a press release on Monday that its vaccine was 79 percent effective at preventing symptomatic Covid-19 infections. The U.S. government’s Data and Safety Monitoring Board (DSMB)—an independent group in charge of overseeing each company’s vaccine trials—took the unusual step of publicly alleging that the announcement was based on outdated information and requested the company submit more recent data.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, broke the issue down in a fairly straightforward manner during an interview with Good Morning America on Tuesday. 

“The issue that the DSMB had is straightforward and very simple: The DSMB had data that they know the company had. When they saw the press release, they said, ‘wait a minute—the data in the press release do not reflect the most recent data that we know you have,’” Fauci said in the interview.

The data AstraZeneca based its initial announcement on came from trials in mid-February. The updated data—from trials conducted earlier this month—revealed that the vaccine is 76 percent effective; a slight dip of three percent from its initial claim. AstraZeneca claimed that the vaccine is still effective, and that efficacy in people 65 and older actually increased from 80 percent to 85 percent.

This whole situation is just really weird, especially since the vaccine still meets the Food and Drug Administration’s (FDA) approval requirements of at least 50 percent effectiveness. I guess they believed a C+/B- looked better on paper than a regular old C?


The controversy comes at a less than ideal time for the company’s vaccine which has been used predominantly in European countries so far. 13 countries suspended the use of the vaccine earlier this month due to unsubstantiated claims that it was responsible for blood clots. The European Medicines Agency had to reassure those countries last week that the vaccine was effective and safe for use.

In a world that basically gets most of its information from headlines, it’s not a good look for so much controversy to surround a vaccine that a significant chunk of the population is already giving side-eye to. Especially a controversy like this which was both unnecessary and completely avoidable.


The former president signed a deal with AstraZeneca for 300 million doses of the vaccine, and the company still intends to move forward with its plan to seek emergency authorization from the FDA to distribute the vaccine in April.

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Dr Emilio Lizardo

That may (or may not) be statistically significant, but I doubt it is clinically significant. Would like to see the error bars on it.

Besides, it was previously reported that it was 100% effective at preventing death and severe illness and I haven’t seen that disputed anywhere. If a vaccine can turn COVID into just another common cold virus, that’s more than good enough.