AstraZeneca CEO Pascal Soriot

A vaccine participant in the United Kingdom developed a rare inflammatory disease, causing AstraZeneca to pause its Phase 3 COVID-19 trials, STAT first reported Wednesday.

AstraZeneca CEO Pascal Soriot said during a call with investors Wednesday — a day after the trial was shut down temporarily — that the volunteer was being treated for transverse myelitis and was expected to be discharged from a hospital soon.

Soriot also revealed that the massive trial testing a vaccine developed in conjunction with the University of Oxford was halted in July, too, after another participant showed neurologic symptoms. 

A spokesperson for AstraZeneca said the current pause was triggered by its standard review process “to allow review of safety data.” Part of that process is determining whether the side effects were caused by the injection or something else, as was the case in July when multiple sclerosis was diagnosed in the volunteer.

Both Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, and British Health Secretary Matt Hancock said Wednesday that short-term stoppages in vaccine testing were par for the course.

“It’s not uncommon at all,” Fauci told “CBS This Morning.” “It’s really one of the safety valves that you have on clinical trials such as this.”

Hancock said pausing the trial wasn’t a sure sign of a setback.

Regardless of what happens with AstraZeneca’s trial, one of only three would-be vaccine makers in the third stage of clinical trials in the U.S., Fauci continued to warn that the right vaccine will take time.

He said Tuesday that any vaccine probably won’t be ready before election day, even as the Centers for Disease Control and Prevention asked states to prepare distribution sites. Moderna and Pfizer are only just now starting final-phase patient enrollments.

“It’s unlikely we’ll have a definitive answer” by Nov. 3, Fauci said during an appearance at a virtual research conference Tuesday. A better bet, he said, is that a vaccine might be approved for distribution by the end of the year.