CHICAGO (Reuters) — Results of AstraZeneca’s U.S. COVID-19 vaccine trial are being reviewed by independent monitors, and emergency authorization could come in about a month, a top U.S. official told Reuters on Monday.

The independent monitors are analyzing data from the 32,000-person U.S. study to determine whether the vaccine is safe and effective. If the results are positive and all goes well, the U.S. Food and Drug Administration would review the data and issue the authorization, Dr. Francis Collins, director of the National Institutes of Health (NIH), said in an interview.

Collins estimates that the FDA would need about three weeks to analyze the trial data, after which an expert advisory panel will meet and vote on whether to recommend authorization.

Independent monitoring boards periodically review data during clinical trials to make sure no safety problems crop up, and can halt studies early if it determines a drug or vaccine is likely to fail or is clearly going to be a success.

The AstraZeneca vaccine, developed with the University of Oxford, has been authorized for use in the European Union and many countries based on separate trial data. U.S. regulators have been waiting for the U.S. data.

Several EU countries have halted administering the AstraZeneca vaccine after reports from Denmark and Norway of possible serious side effects, including bleeding and blood clots.

Asked about those issues, Collins said he has not personally seen the data but has been “pretty reassured” by statements from European regulators that the problems could be occurring by chance, and are not related to the vaccine.

With so many people being vaccinated, Collins said, some are bound to experience a blood clot around the same time they receive a vaccine.

“It’s not clear at all” that people who receive the vaccine get blood clots at an increased rate, Collins said, adding “there may be a bit of an overreaction to something that is unrelated to the vaccine itself.”

A World Health Organization expert said on Monday he sees no association between reports of blood clots and the AstraZeneca vaccine and urged people not to panic.

Asked about the emergence of more contagious viral variants that could evade vaccine protection, Collins said studies so far suggest that currently authorized vaccines from Pfizer Inc, Moderna Inc and Johnson & Johnson will be protective.

“We do not feel that we are in a difficult situation that requires immediate action in the U.S., but we’ve got to watch this really closely,” said Collins, a geneticist who has led the NIH since 2009.

COVID-19 vaccine makers have already started work on booster doses of their shots that specifically target a concerning variant first discovered in South Africa. Those would be ready by the end of 2021 or early 2022.

It will not be clear until this summer or fall whether a booster dose is necessary, Collins said.

“I really hope that doesn’t happen, but I think we would be foolish not to plan for that just in case, and so planning is happening,” he said.

Reporting by Julie Steenhuysen in Chicago and Michael Erman in New York; Editing by Peter Henderson and Bill Berkrot.

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