Why U.S. Approval of the AstraZeneca Covid-19 Vaccine Is Taking So Long

An unprecedented public exchange with a data review board is the latest of AstraZeneca-Oxford vaccine’s hurdles

A vial of AstraZeneca vaccine sits on a white surface next to a capped syringe
AstraZeneca's vaccine is approved for use in over 20 countries. Photo by Joaquin Gomez Sastre/NurPhoto via Getty Images

On the evening of March 24, AstraZeneca announced its Covid-19 vaccine is 76 percent effective at preventing symptomatic disease, based on its Phase III trial of over 32,000 participants mostly in the United States. The results concluded a whirlwind of news stories about the AstraZeneca vaccine in March.

At this point, the vaccine has been approved for use in the United Kingdom and several European Union countries since December. It has not yet been approved in the U.S. because the Food and Drug Administration (FDA) asked the company to provide results from a large-scale trial, Umair Irfan reports for Vox. Experts have expected the data to show that the vaccine is safe and effective, but worry how AstraZeneca’s recent hurdles might impact its reputation around the world.

“I think the way that the ship will be righted is by having the FDA’s scrutiny,” says biostatistician Stephen Evans of the London School of Hygiene & Tropical Medicine to Smriti Mallapaty and Ewen Callaway at Nature. Evans expects the vaccine will be approved when the FDA is able to review the raw data.

On March 18, the European Medicines Agency (EMA) completed its review of the AstraZeneca vaccine, which is made in partnership with Oxford University, and concluded that it is safe and effective, BBC News reports. The E.U.’s medical regulation agency had revisited the vaccine’s safety because, out of about 17 million people who had gotten the shot by early March, 37 people developed unusual blood clots.

More than 20 countries suspended use of the vaccine while the EMA reviewed the cases, Kai Kupferschmidt and Gretchen Vogel report for Science magazine. Most countries resumed vaccine use after the EMA concluded that it is safe, but last week Friday, Norway extended its suspension of the vaccine until April 15, Gwladys Fouche and Terje Solsvik report for Reuters. Norwegian officials hope more data about the cause of the blood clots will become available soon.

On March 22, AstraZeneca released its initial results of the Phase III trial, which showed slightly higher effectiveness at preventing Covid-19 than the latest results. The results were long-awaited. The FDA asked the company to conduct a larger trial in order to get clearer data than they gathered in their first rounds of testing. In the first trials in the U.K., some participants unexpectedly received half-doses of the first shot in the vaccine, and the early trials did not include enough people older than 65, reports the Washington Post.

By the morning of March 23, officials at the National Institute of Allergy and Infectious Diseases released a letter from its data and safety monitoring board that's been examining the AstraZeneca trial, Andrew Joseph reports for STAT News. The letter stated that AstraZeneca had used outdated data to reach its efficacy number. The move was unprecedented; usually, monitoring boards keep their correspondence with companies private.

“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,” says Anthony Fauci, director of the NIAID, to STAT News. “In my mind, it’s an unforced error by the company.”

AstraZeneca explained the initial results included data gathered until February 17, per Nature.

Within 48 hours, AstraZeneca released its revised results with updated data. According to the statement, the vaccine has 76 percent efficacy at reducing symptomatic Covid-19 overall, and 85 percent efficacy in people 65 years old and older. A specific review of the 32,000 participants in the U.S. trial found no cases of the unusual blood clots that caused hesitation in Europe, per STAT News.

“The benefits of these results will mainly be for the rest of the world, where confidence in the AstraZeneca vaccine has been eroded,” said Evans to the New York Times.

AstraZeneca plans to submit the data for emergency use authorization in the coming weeks and then the FDA additional time to review the data and make its decision.

The AstraZeneca vaccine may not have a large role in vaccinating people in the United States because the three companies already approved to supply vaccines in the country agreed to provide enough doses for anyone who wants one this year. But AstraZeneca is participating in the COVAX program to provide doses to low- and middle-income countries for no profit, and FDA approval is a global gold-standard for safety of medications.

“At the end of the day, the FDA looks at the data, not the press releases,” says the FDA’s former chief scientist Jesse Goodman to Vox. “Looking at that data and doing their own analysis is what’s going to determine whether this vaccine gets an [emergency use authorization], whether the benefits outweigh the risk.”

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