By Jenny Strasburg, Thomas M. Burton & Joseph Walker

AstraZeneca PLC said it would update and reissue later this week efficacy data from human trials of its Covid-19 vaccine after U.S. officials took the rare move of publicly questioning their accuracy—the latest misstep by the British drug giant as it struggles to get its shot into American arms.

In an early-morning statement, the National Institute of Allergy and Infectious Diseases said it had been informed by the independent data-monitoring board working with AstraZeneca on the U.S. trials that the drug company might have used out-of-date information in its public disclosure of the vaccine’s effectiveness. The day before, AstraZeneca released interim data from a large-scale U.S. trial that it said found its Covid-19 vaccine to be 79% effective in preventing symptomatic disease.

The results served as a short-lived vote of confidence in the shot, which has been clouded by uncertainty over previous, confusing efficacy results and large-scale production problems. More recently, reported cases of rare blood clotting in Europe raised concerns about the vaccine’s safety, though European regulators have recommended its continued use. The U.S. trials showed no link between the clotting and the vaccine, and the NIAID statement Tuesday didn’t raise questions about that finding or other safety-related issues.

Despite the reputational cloud, the shot is being rolled out widely outside the U.S., including across Europe where it is a key plank in its vaccination drive. Regulators there and in dozens of other countries have approved the shot for use. The U.K. has administered more than 11 million doses. Dr. Anthony Fauci, President Biden’s top medical adviser and the director of NIAID, said Tuesday he still thinks the AstraZeneca shot is a good vaccine.

NIAID said the independent data monitoring board working with AstraZeneca in conducting its trials raised concerns about the company’s disclosures and had urged the drugmaker to work with it to ensure that the most accurate, up-to-date efficacy data would be made public.

According to senior U.S. officials familiar with the matter, the data that the monitoring board was reviewing showed efficacy of about 70% to 79%, a number that shifted daily based on new data. In recent days, the monitoring board had debated with AstraZeneca what number to use in any public disclosure, according to one of these officials, and it was adamant that the number should not be more than 75%.

AstraZeneca, which developed the vaccine in partnership with the University of Oxford, said in its own statement Tuesday that its disclosure on Monday was based on an interim analysis with a data cutoff of Feb. 17. It said that it would “immediately engage” with the monitoring board to share its analysis of “the most up-to-date efficacy data.” AstraZeneca said it would issue results of that analysis in the next two days.

The NIAID statement was a significant deviation from what are usually carefully scripted drug trial releases—done in coordination with medicines regulators and with regard to how they might affect public perception of safety, as well as how they might affect a company’s share price.

Dr. Fauci said the data-monitoring board felt AstraZeneca’s press release about the results on Monday didn’t reflect the most recent and accurate data that board members had seen, and, “They were concerned about it and they were really quite harsh about it.”

He said a big factor in the decision to go out with a NIAID statement was that the agency had issued its own press release containing the AstraZeneca claims the same day. “So, we felt it was absolutely necessary that we make a nonpejorative, nonaccusatory statement to say, ‘Hey, you better get together with the [data monitoring board] and work this out,’ ” he said.

Once AstraZeneca includes the more recent data, Dr. Fauci added, the effect on the shot’s reported 79% effectiveness will probably be modest. “That’s the ironic part about it,” he said. “I mean, this is kind of unfortunate that this happened because at the end of the day, it’s still a good vaccine.”

The uncertainty of the shot’s efficacy clouds AstraZeneca’s timeline for emergency use authorization in the U.S. It had said it hoped to apply to the Food and Drug Administration for authorization quickly.

The pushback from Washington is also the latest in a series of stumbles by AstraZeneca, one of the world’s biggest pharmaceutical companies, but one that has little experience in vaccines. The company teamed up with the University of Oxford early last year and promised to roll out 3 billion doses of the two-dose shot this year, without profit. But since that pledge, the company has struggled to keep its vaccine trial and production efforts on track.

AstraZeneca released U.K. human trials last year, but data was muddled by confusing and incomplete explanations for a range of efficacy levels. AstraZeneca then shocked European governments when it said it would miss by a wide margin its delivery promise of doses in the first quarter. The company had suffered manufacturing problems at a plant in Europe. Later, it promised to make up for the shortfall by importing doses, but then backtracked on that, too.

AstraZeneca has pushed back against criticism and defended the shot. Executives, including Chief Executive Pascal Soriot, have repeatedly pointed out that AstraZeneca is making more vaccines than any other drugmaker and is doing so without profiting.

The latest hit came earlier this month with reports of a small number of serious blood clots, including several reported deaths, in recently vaccinated Europeans. Several big countries, including France and Germany, paused their use of the shot until Europe’s main medicines regulator investigated the incidents. Last week, that regulator, the European Medicines Agency, said it didn’t find evidence of a link between the clotting problems and the vaccine, but also couldn’t rule one out. It recommended a new warning be provided to healthcare professionals and the public about the AstraZeneca shot, to alert them of the need to monitor carefully for potential severe blood clots.

The relationship between AstraZeneca and U.S. officials has been tense in the past. The FDA felt that AstraZeneca hadn’t informed it quickly enough when a participant in the U.K. trials fell ill and that the company later was slow to provide follow-up information.

The FDA at the time paused U.S. trials, which were just getting under way. The trials were later resumed, but after a weeks-long delay that pushed back significantly AstraZeneca’s ambitions of getting its shot quickly approved for use in the U.S. As AstraZeneca responded to FDA questions during the U.S. trial pause, officials inside the agency got the impression the company was struggling to get its arms around the process of rapidly pulling together the necessary information, citing a senior U.S. administration official.

Mr. Soriot defended the company’s disclosure of the illness at the time and its interactions with the FDA.