An updated company analysis of the coronavirus vaccine developed by AstraZeneca and the University of Oxford showed that the two-shot regimen was robustly effective – 76% at preventing symptomatic illness – according to a news release from the drugmaker late Wednesday.

The finding, only slightly lower than results announced days earlier, underscores that the vaccine being widely used by many countries appears to be a powerful tool to help end the pandemic. No severe cases of illness were reported in study volunteers who received the vaccine. Among people 65 and older, the vaccine was 85% effective, the company reported.

The new data may not resolve challenges that the vaccine and the company face in the United States, because repeated missteps have sown confusion and distrust that may result in slower and closer scrutiny of the data.

AstraZeneca and Oxford’s announcement Monday that their vaccine was 79% effective in a 32,000-person trial in the United States buoyed the company’s stock price and impressed government officials.

The fraught story of the vaccine then took a dramatic turn when an independent data-monitoring committee took the highly unusual step of writing late Monday to company and government officials, airing concerns.

The expert physicians, biostatisticians and ethicists on the Data and Safety Monitoring Board that oversee trials have an inside view of the research and are charged with maintaining patient safety and scientific validity. Their communications with companies typically take place in private.

But in the letter, obtained by The Washington Post, the committee revealed that after several meetings and requests for more recent data, the company had chosen to present earlier, now-outdated data to the world that cast its vaccine in the most favorable light. The dispute was about whether the company had selected data to paint the most flattering picture of how effective the vaccine was, not about whether the vaccine worked.

“Decisions like this are what erode public trust in the scientific process,” the committee of outside experts wrote in the letter.

The National Institutes of Health issued a statement early Tuesday, urging the company and data committee to work together to “ensure the most accurate, up-to-date efficacy data be made public as quickly as possible.”

Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said in an interview Tuesday the irony of the situation is that the vaccine probably works well. Many U.S. scientists have watched the drama unfold with disbelief.

The data has not been published or peer-reviewed, but AstraZeneca said Wednesday night in its statement that the new analysis had been presented to an independent data board.

“The primary analysis is consistent with our previously released interim analysis, and confirms that our COVID-19 vaccine is highly effective in adults, including those aged 65 years and over,” Mene Pangalos, executive vice president of biopharmaceuticals research and development at AstraZeneca, said in a statement. The company plans to submit an emergency use authorization in the coming weeks, and is prepared to send out 30 million doses upon authorization.

Before this week’s drama, AstraZeneca and Oxford had reported confusing results from a U.K. trial last fall. While the initial results were positive, with up to 90% efficacy in one group of participants and 62% in another, more details about how the trial had been conducted leaked out over days, turning a positive result into a hard-to-interpret mess and an ongoing news story.

Supply issues with the European Union have created further friction.

A rare blood clotting syndrome that resulted in some deaths caused the vaccination effort to be paused in some countries as experts explored whether there it may have been caused by the vaccine. Even as vaccination efforts have restarted, some regulators have said they could not rule out a possible link.

The latest twist in the saga, a technical discussion over how effective the vaccine is in the U.S. trial, doesn’t threaten the conclusion that the vaccine is effective. But it has become yet another avoidable challenge for the company. The vaccine still looks effective, but the reputational hit from the back and forth with the data committee could trickle down to undermine confidence in the vaccine.

“This represents another hiccup for AstraZeneca in terms of public perception,” Yaron Werber, an equity analyst at the firm Cowen wrote in a research note Tuesday. “In our view, AstraZeneca’s vaccine [is] unlikely to play a large role in vaccinating the U.S. population given the swift rollout of the three currently authorized vaccines and the controversy around the AstraZeneca data.”

Regulatory approval in the United States is a crucial event for the company, although it is increasingly uncertain whether or how the vaccine will fit into the portfolio as supply of other vaccines increases.

But the United States is not only a large market; its regulatory decisions are often a benchmark for the rest of the world.

“In spite of the drama, this is still a big win for global health,” David Benkeser, a biostatistician at the Emory University Rollins School of Public Health, said in an email.

Although other countries have already authorized the vaccine, a positive U.S. decision could help fuel global uptake. Because AstraZeneca has vowed to sell its vaccine with no profit in low- and middle-income countries, even after the pandemic is over, the U.S. market also represents one of the major opportunities for the company to make a profit.

“We will, at some stage, sell it commercially, at commercially reasonable prices in the wealthy countries and not-for-profit in the poorer countries in the world,” Pangalos said in an interview Monday.

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