Federal health officials said early Tuesday that the results of a US study of AstraZeneca’s Covid-19 vaccine may be based on “out of date information” that “may have provided an incomplete view of the efficacy data,” which casts doubt on an announcement on Monday leaves This is good news for the Anglo-Swedish company as well as for the global vaccination campaign.

In an extremely unusual statement released after midnight, the National Institute of Allergy and Infectious Diseases announced that the Data and Safety Monitoring Board, an independent panel of medical experts from the National Institutes of Health, was responsible for overseeing the US study of AstraZeneca contributed to informing government agencies and AstraZeneca late Monday that it was “concerned” about information the company released that morning.

The Institute asked AstraZeneca to work with the Monitoring Committee “to review the efficacy data and ensure that the most accurate and up-to-date efficacy data is published as soon as possible”.

AstraZeneca didn’t immediately return a request for comment early Tuesday.

In a press release on Monday announcing the results of the U.S. study, the company said the vaccine against Covid-19 developed with Oxford University was 79 percent effective, higher than seen in previous studies, and the worst results completely prevented the disease. The long-awaited results were seen as encouraging global confidence in the vaccine, which was shaken this month when more than a dozen countries, mostly in Europe, temporarily stopped using the shot because of concerns about possible rare side effects.

In the past few days, the monitoring committee’s analysis has been delayed several times as the committee had to request revised reports from those handling experimental data on behalf of the company, according to a person familiar with the matter who was not empowered to discuss it publicly.

Companies that sponsor drug or vaccine studies usually wait for the monitoring panel to do analysis and conclude that the study has provided a response before disclosing the study results. During the trial, a non-blinded statistical analysis group, isolated from the company, acts as an intermediary to handle data requests and many other interactions with the supervisory board.

Company executives are blind to the results of the study until the Monitoring Board reports their study data back to them. The Monitoring Board eventually sent the results of the study to AstraZeneca in a weekend meeting, leading to the company’s announcement on Monday morning.

An AstraZeneca spokeswoman, whose name the company refused to reveal, said last week it was “totally wrong” that the test data had formatting problems or was not properly transmitted to the regulator.

“As is so often the case,” said the spokeswoman, “monitoring bodies” can request new or clarifying analyzes of data from the study. This would enable them to ensure the robustness of their provisions. “

Dr. Eric Topol, an expert on clinical trials at Scripps Research in San Diego, said it was “very infrequent” to see such public friction between a monitoring committee and a study sponsor, which are usually close.

Updated

March 23, 2021, 7:01 a.m. ET

“I’ve never seen anything like it,” he said in an interview after the institute’s statement was published. “It’s so, so unsettling.”

AstraZeneca’s relationship with the US authorities has been strong since last year when senior health officials believed the company was not open about the design of its clinical trials, results and safety issues. That skepticism carried over to last week when senior officials from a number of federal health officials became suspicious of why AstraZeneca had not announced data from its US study.

This US trial, which was attended by more than 32,000 participants, was the largest test of its kind for the shot. The results, AstraZeneca released on Monday, came from an interim look at the data after 141 Covid-19 cases occurred in volunteers.

The company has not disclosed how current the data is. If the analysis was done on data from a month or two ago, it is possible that a more recent look may give a different picture of the vaccine’s effectiveness and safety. The company has announced that it will provide the Food and Drug Administration with a more comprehensive and up-to-date dataset than announced on Monday. Although no clinical study is large enough to rule out extremely rare side effects, AstraZeneca reported that its study did not identify any serious safety issues.

The new data may have arrived too late to make a big difference in the United States, where the vaccine has not yet been approved and is not expected to be available until May. By then, federal officials say, there will be enough vaccine doses for all adults in the country from the three already approved vaccines: Pfizer-BioNTech, Moderna, and Johnson & Johnson.

Even so, the better-than-expected results have been seen as an encouraging turn for AstraZeneca’s shot, whose low cost and simple storage requirements have made it an important part of the quest to vaccinate the world.

The results were also believed to allay concerns about the AstraZeneca vaccine in Europe. Regulators there said the shot was “safe and effective” last week after conducting a review after a small number of people who had recently been vaccinated developed blood clots and abnormal bleeding. The US study found no evidence of such problems, although some real-world safety issues can only be identified when a drug or vaccine is widely used.

Millions of people have received the AstraZeneca shot worldwide, including more than 17 million in the UK and the European Union, almost all without serious side effects. To increase public confidence, many European political leaders have received the injections in the past few days. The AstraZeneca vaccine was also given to executives in South Korea, Taiwan and Thailand last week.

AstraZeneca said Monday it will continue to analyze the new data and prepare to apply for an emergency permit in the US in the coming weeks. The vaccine has already been approved in more than 70 countries, but clearance by American regulators would bolster its global reputation.

The Infectious Disease Institute’s testimony comes after a series of mistakes and communication errors made by AstraZeneca last year that undermined the confidence of American officials in the company.

Last summer, at least some senior FDA officials only learned from news that AstraZeneca suspended its Phase ⅔ vaccine study in the UK after a participant developed neurological symptoms. Then, in September, after another participant in the UK study developed similar symptoms, AstraZeneca stopped its trials worldwide but failed to notify US authorities immediately.

The US study was suspended for seven weeks last fall, partly because AstraZeneca was slow to provide the FDA with evidence that the vaccine had not caused the neurological symptoms. Investigators eventually concluded that the diseases could not be linked to the vaccine. Still, the delay was a major reason AstraZeneca has lagged behind the three other manufacturers whose vaccines have received emergency approval in the US.