The us food and drug administration has widened its probe into an adverse event involving a patient on a trial for the coronavirus vaccine that astrazeneca is developing with the university of oxford, according to people briefed on the matter.

The fdas move, first reported by reuters, stems from a trial participant in the uk falling ill with unexplained neurological symptoms, previously believed to be consistent with transverse myelitis, which caused trials to be halted last month.

Trials in the uk, brazil and south africa, which were all paused after the adverse event was reported, have been deemed safe to resume, astrazeneca said on thursday.

Regulators in each individual country determine when trials can start and they do this in their own timeframe, said the drugmaker. we are continuing to work with the fda to facilitate a review of the information needed to make a decision regarding resumption of the us trial.

The fda is obviously being thorough in its review, one of the people briefed on the matter said.

The revelation came as the european medicines agency is expected to introduce rolling reviews for potential coronavirus jabs, starting with astrazenecas product on thursday, according to people familiar with the matter.

The move could speed up the assessment and marketing of any potential inoculations. drugmakers and regulators have been under intense political pressure especially in the us from president donald trump, who is seeking re-election next month to deliver a vaccine as soon as possible.

The financial times reported on wednesday that the chief executive of moderna therapeutics, which is developing a potential jab, said the vaccine would not be ready before the election.

On tuesday, stephen hahn, fda commissioner, said his agency would stick to its vaccine approval criteria despite mr trumps pressure, the ft reported.

The regulation of vaccines, which are technically biologics, falls into the emas remit, including for the uk, which is in a transition period as it departs the bloc.

However, the uk said in august it would depart from the emas regulatory orbit in order to grant any efficacious jab temporary approval, if necessary.

Pharmaceutical products will be regulated by the uks medicines and healthcare regulatory agency alone after december 31. astrazeneca is in talks with mhra over rolling reviews, according to one of the people briefed on the matter.

Multiple covid-19 vaccine candidates, backed by large amounts of public cash, are undergoing phase 3 testing the last step before they go to regulators for approval. timelines have been compressed from years to months.

The fda declined to comment. the ema confirmed on thursday afternoon that it would go ahead with a rolling review of astrazenecas candidate.

This article has been updated to clarify the unexplained neurological symptoms were previously thought to be associated with a condition known as transverse myelitisand add the emas comment