AstraZeneca revises down its vaccine efficacy in a huge US trial, to 76% from 79%, following concerns from Fauci and other experts that the results were outdated

• AstraZeneca says its vaccine was 76% effective at preventing symptomatic COVID-19 in its US trial.
• That was slightly below an efficacy that experts, including Fauci, said was based on outdated data.
• The updated result, announced Thursday, still found it 100% effective at preventing severe COVID-19.

AstraZeneca has updated its US COVID-19 vaccine trial results following concerns from Dr. Anthony Fauci and a panel of experts that the drugmaker had presented outdated data.

The updated results, released Thursday, showed AstraZeneca's shot was 76% effective at protecting against symptomatic COVID-19, 15 days after the second dose of the two-dose vaccine. The company had said on Monday that the vaccine was 79% effective in the trial, which involved more than 32,000 people.

The vaccine still worked well across all age groups in the updated results, with an estimated effectiveness of 85% in people over 65 years old, AstraZeneca said.

It was still 100% effective at preventing severe illness and hospitalization, and there were no safety concerns, AstraZeneca said.

The small change seen in the top-line efficacy figure, to 76% from 79%, may be negligible: The actual effectiveness could lie between 68% and 82%, according to the numbers provided.

Isaac Bogoch, an associate professor of infectious diseases at the University of Toronto, said on Twitter on Thursday that the vaccine "still looks good."

Read more: COVID-19 Vaccine Tracker: AstraZeneca's shot proves safe and effective, and is headed to the FDA

AstraZeneca's update followed concerns from an independent expert safety panel, called the Data and Safety Monitoring Board, that the US trial results released Monday could be partially based on "outdated data."

Fauci, who heads the National Institute for Infectious Diseases and oversees the DSMB, told STAT on Tuesday that AstraZeneca had initially made an "unforced error."

"If you look at it, the data really are quite good, but when they put it into the press release, it wasn't completely accurate," Fauci told "Good Morning America" on Tuesday.

Full details of the clinical trial are not yet available. AstraZeneca said Thursday that it planned to submit to a peer-review publication "in the coming weeks."

AstraZeneca's trial results open the door for emergency authorization in the US, which could revive the shot's reputation worldwide, including in Europe, where more than 18 countries temporarily suspended it while regulators investigated potential side effects.

"We look forward to filing our regulatory submission for Emergency Use Authorization in the US and preparing for the rollout of millions of doses across America," Mene Pangalos, the executive vice president at AstraZeneca, said.