AstraZeneca resumes Covid-19 vaccine trials in the U.K.

A large, United Kingdom-based Phase 2/3 study testing a Covid-19 vaccine being developed by AstraZeneca has been restarted, according to a statement from the company. News that the trial is resuming comes four days after the disclosure that it had been paused because of a suspected serious adverse reaction in a participant.

A spokesperson for AstraZeneca told STAT that at this point, only the trial in the U.K. has been resumed. The company is also conducting Phase 2/3 or Phase 3 trials in the U.S. and Brazil, as well as a Phase 1/2 trial in South Africa.

“The Company will continue to work with health authorities across the world and be guided as to when other clinical trials can resume to provide the vaccine broadly, equitably and at no profit during this pandemic,” the spokesperson, Michele Meixell, wrote in an email.

Saturday’s statement from AstraZeneca said the independent U.K. investigation into the event has concluded and it advised the Medicines Health Regulatory Authority, Britain’s equivalent of the Food and Drug Administration, that it was safe to resume the trial. The MHRA concurred and gave the green light for the trial to restart.

The illness that triggered the international pause, which occurred in a woman who was in the vaccine arm of the U.K. trial, has not been officially disclosed, though AstraZeneca CEO Pascal Soriot told a group of investors on Wednesday that her symptoms were consistent with transverse myelitis, a serious condition involving inflammation of the spinal cord that can cause muscle weakness, paralysis, pain and bladder problems.

The AstraZeneca statement said information about the illness the woman suffered cannot be disclosed. Oxford University, where the vaccine was developed, said in a separate statement that the nature of the illness cannot be revealed “for reasons of participant confidentiality.”

As part of the review process, independent boards overseeing trials of a number of other Covid-19 vaccines were analyzing their own data, looking for cases. There are at least 35 vaccines in clinical trials around the world, nine of which are in Phase 3, the final stage of testing.

It’s not uncommon for clinical trials to be paused. This is the second known hold of studies of the AstraZeneca vaccine. A woman in the U.K. trial was diagnosed with multiple sclerosis in July, but that event, which triggered the first pause, was deemed not to be related to the vaccine.

An AstraZeneca spokesperson previously described the decision as a “routine action which has to happen whenever there is a potentially unexplained illness” in a trial. Still, the pause drew extraordinary attention because of the urgent need for progress on Covid-19 vaccines in the midst of the pandemic.

Correction: An earlier version of this story misstated the stage of the AstraZeneca trial in South Africa. It is a Phase 1/2 trial.