U.S. health officials question AstraZeneca vaccine trial results

“Decisions like this are what erode public trust in the scientific process."

Health care professionals prepare doses of the AstraZeneca coronavirus vaccine in Milan on Monday, March 22, 2021. (Alessandro Grassani/The New York Times)

Only hours after AstraZeneca announced encouraging news about the effectiveness of its COVID-19 vaccine Monday, a group of medical experts charged with monitoring the company’s clinical trial made a highly unusual accusation: AstraZeneca had essentially cherry-picked data to make its vaccine look better.

Related Links

The accusation, in a two-page letter sent Monday to the company and federal officials, was a fresh blow to the credibility of a vaccine whose low price and relatively easy storage have made it critical to the global fight against the coronavirus pandemic.

The private letter, which was described by people who have read it, castigated AstraZeneca for jeopardizing the integrity of a closely watched clinical trial.


“Decisions like this are what erode public trust in the scientific process,” the oversight board wrote.

The letter prompted the National Institute of Allergy and Infectious Diseases to issue a sharply worded statement Tuesday shortly after midnight, disclosing the panel’s concerns.

The fight is about the degree of effectiveness of a vaccine that is undisputably effective.

While AstraZeneca said Monday that its vaccine appeared to be 79% effective at preventing COVID-19, the panel of independent experts said the actual number may have been between 69% and 74%. The mass availability of a vaccine with even a 69% efficacy rate could help the world conquer the coronavirus.

Fears that the vaccine might trigger rare but serious side effects had led more than a dozen countries, mostly in Europe, to temporarily suspend the use of the shot. European regulators last week affirmed the vaccine’s safety. The results from the U.S. trial Monday — providing the cleanest, most complete picture of the vaccine’s efficacy — seemed to validate the vaccine’s and made it look more effective than in earlier trials.

In short, it bolstered the credibility of arguably the world’s most important vaccine, one that has been authorized for use in more than 70 countries. But the overnight announcement from the institute immediately raised a new set of questions about it and AstraZeneca.


“If they keep making these unforced errors, then that’s going to derail confidence, and that will really affect our ability to combat this pandemic,” said Dr. Peter J. Hotez, a vaccine expert at the Baylor College of Medicine.

Get's browser alerts:

Enable breaking news notifications straight to your internet browser.


This discussion has ended. Please join elsewhere on