Health and Science

AstraZeneca revises Covid vaccine data with lower efficacy rate after accuracy questions

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Key Points
  • AstraZeneca issued updated phase three trial data for its Covid-19 vaccine on Wednesday after facing criticism earlier this week over a preliminary report from its U.S. study.
  • The company now says its vaccine is 76% effective in protecting against symptomatic cases of virus. A release issued on Monday reported a symptomatic efficacy rate of 79%.
  • AstraZeneca reiterated Wednesday that the vaccine was "well tolerated" among participants and that no safety concerns were identified.
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AstraZeneca revises vaccine data efficacy rate after oversight board rebuke

AstraZeneca issued updated phase three trial data for its Covid-19 vaccine on Wednesday after facing accuracy questions earlier this week surrounding a preliminary report from its U.S. study.

The company now says its vaccine is 76% effective in protecting against symptomatic cases of virus. A release issued on Monday reported a symptomatic efficacy rate of 79%. The updated report maintains that the shot is 100% effective against severe disease and hospitalization.

A slate of U.S. health officials criticized the company in recent days for what some claimed was data cherry-picking in an effort to make the results appear more favorable.

The National Institute of Allergy and Infectious Diseases revealed on Tuesday it had been informed the U.K.-based company may have included information from its U.S. results that provided an "incomplete view of the efficacy data."

AstraZeneca said at the time the figures were based on a "pre-specified interim analysis" and vowed to share updated analysis in the coming days.

The Corona vaccine of the Swedish-British manufacturer AstraZeneca is stored in a GP practice.
Nicolas Armer | picture alliance | Getty Images

Dr. Anthony Fauci, White House chief medical advisor and director at the NIAID, called the situation "unfortunate" and said it was likely AstraZeneca would issue a modified statement.

"This is really what you call an unforced error because the fact is this is very likely a very good vaccine," Fauci told ABC's Robin Roberts on "Good Morning America" on Tuesday. "This kind of thing does ... really cast some doubt about the vaccines and maybe contribute to the hesitancy. It was not necessary."

The updated results include data collected from 190 symptomatic cases, across more than 32,000 participants — an increase of roughly 50 symptomatic cases studied compared with the data set released on Monday.

The findings suggest the vaccine is more effective in patients aged 65 and older than previously understood, with a newly reported efficacy rate of 85% for that population, up from a previously stated 80%.

AstraZeneca reiterated Wednesday that the vaccine was "well tolerated" among participants and that no safety concerns were identified.

AstraZeneca faced a separate backlash in recent weeks over reports of blood clotting in conjunction with its vaccine, which is already approved and in use by dozens of countries around the world. Several European nations suspended, then resumed, use of the vaccine after independent safety reviews.

—CNBC's Berkeley Lovelace Jr., Sam Meredith and Steve Kopack contributed to this report.

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