Inquiry Begins Into AstraZeneca’s Vaccine Trial

A participant in the company’s late-stage coronavirus vaccine trial reportedly developed severe neurological symptoms. Now experts must assess whether the vaccine was responsible.

By Katherine J. Wu

Scientists on Wednesday praised the decision by AstraZeneca to suspend its late-stage coronavirus vaccine trials and begin a safety review after learning that a participant had developed a serious neurological condition. Dr. Francis Collins, the director of the National Institutes of Health, testifying at a Senate hearing on Wednesday, said the step “ought to be reassuring.”

The results of the safety review, to be conducted by an independent board of experts, will help determine if the participant’s condition was a reaction to the vaccine candidate or merely coincidental, and are expected to heavily influence whether and when trials might resume.

But many details about the trial’s suspension and the event that triggered it remain murky. Researchers do not yet know what caused the volunteer’s symptoms, how long the evaluation process will take or what the consequences might be.

Part of the review will include generating a timeline of the participant’s symptoms to see if they match up roughly with when the vaccine was administered. The committee will also investigate other potential causes of the symptoms, in a process of elimination.

After determining whether AstraZeneca’s vaccine is the probable cause, experts will advise the company on whether to resume its trials.

Regulatory agencies like the Food and Drug Administration will also likely collect data and give additional input along the way, said Dr. Mark Goldberger, an infectious disease expert at the Global Antibiotic Research and Development Partnership and a former F.D.A. official.

No further doses of the vaccine will be administered in the interim.

In early-stage trials, AstraZeneca’s vaccine candidate, built from an innocuous virus, known to cause common colds in chimpanzees, that was engineered to carry coronavirus genes, yielded promising safety data in people, although several participants experienced mild or moderate side effects including fevers and aches.

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