AstraZeneca, which is running the global trial of the vaccine it produced with Oxford University, said the trial volunteer recovered from a severe inflammation of the spinal cord and is no longer hospitalized.

AstraZeneca has not confirmed that the patient was afflicted with transverse myelitis, but Nath and another neurologist said they understood this to be the case.

Britain's regulatory body, the Medicines and Healthcare Products Regulatory Agency, reviewed the case and has allowed the trial to resume in the United Kingdom.

AstraZeneca "need[s] to be more forthcoming with a potential complication of a vaccine which will eventually be given to millions of people," said Nath.

"We would like to see how we can help, but the lack of information makes it difficult to do so."

Any decision about whether to continue the trial is complex because it's difficult to assess the cause of a rare injury that occurs during a vaccine trial — and because scientists and authorities have to weigh the risk of uncommon side effects against a vaccine that might curb the pandemic.

"So many factors go into these decisions," Nath said.

Typical seasonal flu vaccination raises the risk of GBS in about one additional case in every 1 million people.

"It's very, very hard" to determine if one rare event was caused by a vaccine, Schaffner said.

trial to continue, Goodman said.

They may also require AstraZeneca to update the safety information it provides to study participants.

It's possible that the volunteer's health problem was a coincidence unrelated to the vaccine, said Dr.

trial.

"There is just so little information about this that it's impossible to understand what the diagnosis was or why the DSMB and sponsor were reassured" that it was safe to continue, Goodman said.

AstraZeneca has said it's unable to provide more information about the health problem, saying this would violate patient privacy, although it didn't say how.

But there's an exceptional need for transparency in a political climate rife with vaccine hesitancy and mistrust of the Trump administration's handling of the COVID-19 response, leading scientists say.

"While I respect the critical need for patient confidentiality, I think it would be really helpful to know what their assessment of these issues was," Goodman said.

There is so much interest and potential concern about a COVID-19 vaccine that the more information that can be provided, the more reassuring that would be."

The FDA will need to balance any possible risks from an experimental vaccine with the danger posed by COVID-19, which has killed nearly 200,000 Americans.

"There are also potential consequences if you stop a study," Goodman said.

If the AstraZeneca vaccine fails, the U.S.