AstraZeneca close to restarting Covid-19 vaccine trial in U.S.

By Zachary Brennan 10/21/2020 11:27 AM EDT

AstraZeneca is likely to restart its late-stage U.S. coronavirus vaccine trial “very soon,” possibly later this week, according to one of the researchers leading the study.

Ann Falsey, an infectious disease doctor at the University of Rochester School of Medicine, said that the Food and Drug Administration and the drug safety monitoring board overseeing the trial are in talks about resuming it. AstraZeneca’s vaccine is one of four that have reached the final stage of testing — Phase III — in the United States.

The company halted all trials of the vaccine worldwide in early September after participants in a U.K. study run by Oxford University developed unexplained neurological symptoms. The company has since restarted that trial and others in Brazil and South Africa.

Falsey’s remarks come amid other signs that the American trial could soon get going — including a draft letter from scientists at Oxford University to their U.K. trial participants.

“We are writing to let you know that the US drug regulatory authority (Food and Drug Administration or FDA) has also now completed their analysis of the information relating to the participants concerned and has come to the same conclusion as the other drug regulators including the MHRA,” said the letter provided by the U.K. Health Research Authority, which was first reported by Reuters. “Vaccination will therefore shortly resume in the USA.”

The agency said it did not know whether the letter had been sent to U.K. trial participants.

AstraZeneca said in a statement that the document is not an AstraZeneca communication and “we cannot verify the content of it. We also cannot comment on a pending FDA decision.”

The FDA declined to comment on the matter.

Second dose questions: AstraZeneca’s vaccine is given as two doses four weeks apart. Since the U.S. trial has been halted for longer than four weeks, it’s unclear what will happen to participants who have received the first shot but not the second. AstraZeneca said it expects “minimal impact based on the trial plans for 2nd dose timing.”

The second dose of a vaccine is often times “more effective if there’s a longer interval between the first and second dose,” Falsey said. But she said it would be up to AstraZeneca to decide how to handle delayed second doses.

What’s next: If the U.S. trial restarts, AstraZeneca will look to finish enrolling 30,000 participants. The ongoing trials in the U.K., Brazil and South Africa have now enrolled almost 20,000 participants, according to Oxford. But Falsey said she did not think that AstraZeneca would seek an emergency authorization in the U.S. based on the trial data from other countries — “the data would have to be incredibly compelling,” she said.

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