Remarkably, the AstraZeneca COVID-19 vaccine trial has been restarted only four days after it was paused.

A spokesperson for AstraZeneca told STAT news that their COVID-19 vaccine trial has been restarted. Currently, however, only the trial in the U.K. has been resumed. The company is also conducting trials in the U.S., Brazil, and 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,” AstraZeneca spokesperson, Michele Meixell, wrote in an email to STAT.

Saturday’s statement from AstraZeneca said the independent review board assessment of the event was finished 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 agreed and allowed the trial to restart.

The illness that triggered the international pause in the clinical trial, which occurred in a woman who received the vaccine in the U.K. trial, has not been officially disclosed by either Oxford University or AstraZeneca. Despite this, 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.

This seems like a rapid turn of events and may signal either an obvious other cause for the adverse event or a willingness for UK regulators to facilitate their own vaccine. It will be interesting to see what the FDA and regulators in South Africa decide.