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U.S. health officials raised concerns early Tuesday that positive results that AstraZeneca announced Monday for its Covid-19 vaccine may have been based on “an incomplete view of the efficacy data” from a clinical trial and relied on “outdated information,” throwing another curveball in the saga of the company’s vaccine.

In a statement issued soon after midnight Tuesday morning, the National Institute of Allergy and Infectious Diseases said it had been informed about the data questions by the data and safety monitoring board auditing the trial. DSMBs consist of independent medical experts who review data produced from clinical trials.

“We urge the company to work with the DSMB to review the efficacy data and ensure the most accurate, up-to-date efficacy data be made public as quickly as possible,” NIAID said.


In an interview Tuesday morning with STAT, Anthony Fauci, the head of the NIAID, said the DSMB raised concerns because it felt the results in a AstraZeneca press release Monday looked more favorable than more recent data from the vaccine study had shown.

“I was sort of stunned,” Fauci said. “The data and safety monitoring board were concerned that the data that went into the press release by AZ was not the most accurate and up-to-date data. That is what the DSMB communicated to AZ in a rather harsh note. Having seen that letter we could not just let it go unanswered.”


Asked why NIAID released its unusual statement, Fauci said, “We just felt we could not remain silent. Because if we did remain silent, we could be understandably accused of covering something up. And we definitely didn’t want to be in that position.”

He added: “In my mind, it’s an unforced error by the company.”

The results released Monday by AstraZeneca came from an interim analysis of a 32,000-volunteer trial through Feb. 17. In a statement Tuesday, the company said it would “immediately engage” with the DSMB “to share our primary analysis with the most up-to-date efficacy data.” The company said it planned to announce results from the primary analysis within 48 hours.

“We have reviewed the preliminary assessment of the primary analysis and the results were consistent with the interim analysis,” the company said. “We are now completing the validation of the statistical analysis.”

The two-paragraph statement from the NIAID opened another chapter in the path of the AstraZeneca vaccine, which was developed along with researchers from the University of Oxford. It came not even 24 hours after the company announced in a press release Monday that its vaccine was 79% effective at preventing symptomatic Covid-19 in a U.S. trial, a result that was better than expected based on earlier trials and appeared to help resolve some questions about the robustness of the vaccine. The company also said the immunization reduced severe Covid-19 and hospitalization by 100%. The results were seen as a final step before the company would apply for authorization from U.S. regulators for its shot, which is already approved in other countries.

The DSMB’s letter, however, said more recent data indicated the vaccine was 69 to 74% effective at preventing symptomatic Covid-19, according to the Washington Post, which obtained a copy of the letter.

“The DSMB is concerned that AstraZeneca chose to use data that was already outdated and potentially misleading in their press release,” the letter says. “The point that is clear to the board is that the [vaccine efficacy number] . . . they chose to release was the most favorable for the study as opposed to the most recent and most complete. Decisions like this are what erode public trust in the scientific process.”

The company’s vaccine had been under scrutiny most recently after European countries paused their rollout last week over safety concerns tied to blood clots, but the European Medicines Agency subsequently said the vaccine’s benefits outweighed its risks and the campaigns restarted.

Based on the trial data released Monday, AstraZeneca said the study identified no new safety concerns. A specific review found no risk of blood clots. The study also did not see a specific type of clot in blood vessels near the brain that the EMA said might be associated with the vaccine. However, this type of clot, called a cerebral venous sinus thrombosis, is so rare it might not be expected to occur in even a large clinical trial.

The NIAID statement Tuesday only cited DSMB concerns about efficacy data, and did not mention safety issues.

The two-dose AstraZeneca vaccine is seen as a great hope to help expand vaccine access around the world because it is less expensive than other Covid-19 vaccines and easier to manufacture and distribute than some others. It is being widely used in Europe and increasingly in Asia.

But the company’s vaccine efforts have been dogged by mishaps and questions about its public announcements. Early on, the U.S. study was stopped for a month-and-a-half because of a neurological condition in one patient that was later determined to be unrelated to the vaccine. In initial trial results announced earlier, the data seemed to suggest at one point that the second dose of the vaccine lowered its efficacy. Some of the earlier confusion stemmed from the company’s unusual strategy of pooling data from clinical trials in its analyses.

The ups and downs with AstraZeneca’s vaccines have increased concerns that the public may turn away from an immunization that could help tame the Covid-19 pandemic, at a time when public health officials are urging people to get inoculated when they have a chance. Fauci said on “Good Morning America” Tuesday the frustration was that “this is very likely a very good vaccine” and that he hoped people would understand the DSMB concerns were an example of one of the many guardrails ensuring the quality of the vaccine development process.

“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 said. “We have to keep essentially trying as hard as we can to get people to understand there are safeguards in place.”

Asked whether he was worried about people’s confidence in the AstraZeneca vaccine and others, Fauci told STAT: “Obviously that’s a concern whenever something like this happens, that it could erode public trust, yes.”

But he stressed that the FDA, when it reviews AstraZeneca’s vaccine for authorization, will make an independent decision.

Helen Branswell and Matthew Herper contributed reporting. 

This story has been updated with comments from AstraZeneca and Anthony Fauci. 

Correction: This story previously misstated the reason for the pause of AstraZeneca’s U.S. clinical trial. 

  • Fauci is a career politician first whose primary objective is self preservation. He is an egomaniac who loves the spotlight . Remember his mask comments that they did not protect you from Covid 19 circa Feb. 2020 when the disease first hit the United States? He obviously knew this to be a lie but he peddled it anyway fearing Trump reprisals and ultimate unemployment. Take anything Fauci says with a grain of salt which will likely provide as much protection against Covid 19 as Astra Zeneca’s vaccine.

  • There are two separate issues in this article. The first is the efficacy of the AZ vaccine. On the first, 74% vs 79%; who cares, any vaccine is better than none. The second is Dr. Fauci’s comments which have been consistently wrong(I don’t blame him though). Unfortunately he talks out of both sides of his mouth on this issue.

  • The modus operandi is clear: push forward an embellished, rosy picture, make sure you sweep under the carpet any annoying negative findings. That’s how some executives have built their careers, even got knighted. I am convinced that there are more problems to be found about AZ’s vaccine.

    If the EMEA think that benefits outweigh the negatives, they should go tell that to the families of those who died because of the vaccine. We are not sheep, for which farmers weigh the upside/downside of administering medication. There are other, safer, more efficacious vaccines out there and people deserve them.

  • Yeah…. I agree with you Dr. Faucci. Using the outdated info isn’t really that great! Much like your prediction of only 30,000 – 60,000 US death’s you made last year it was, I believe

    • Actually I heard it was 200-300K in one of Faucci’s modeling reports which is a bit closer yet below the half million. Everyone’s a critic, even when he stated that number.

  • Fauci and the CDC know that this vaccine was not good. That’s why they built it up in the press, only to wait until they showed “humanitarian efforts ” to give to Canada and Mexico…to show that they found something different.

    • Did you read it? The preliminary statistics were slightly better. They chose to communicate that instead of the overall. No one is forcing any country to take the vaccine from the US. This is NOT politics-stop it. People’s lives are at stake! Wait for the accurate information. Please!

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