Clinical trials of a potential COVID-19 vaccine developed by AstraZeneca and the University of Oxford have resumed after a six-day pause.

The trials were paused due to “potentially unexplained illness” in the United Kingdom.

Both AstraZeneca and its partners, the University of Oxford researchers said the trials have resumed.

AstraZeneca said the resumption of trials followed the all-clear from British regulators.

“Clinical trials for the AstraZeneca Oxford coronavirus vaccine, AZD1222, have resumed in the UK following confirmation by the Medicines Health Regulatory Authority (MHRA) that it was safe to do so,” the company said in a statement.

In a release, Oxford University said the study vaccines had been administered to some 18,000 patients as part of the trial.

“In large trials such as this, it is expected that some participants will become unwell and every case must be carefully evaluated to ensure careful assessment of safety,” the release said.

Oxford University researchers said they were unable to disclose the patient’s medical information due to “participant confidentiality.”

An independent safety review was conducted Sept. 6 during what was referred to as a “routine action” to maintain the “integrity of the trials.” It concluded on Saturday.

On Thursday, a spokesperson for AstraZeneca said the brief pause was triggered after one woman developed “severe neurological symptoms” after taking the experimental COVID-19 vaccine.

AstraZeneca said the company’s “standard review process triggered a study pause to vaccination across all of our global trials to allow the review of safety data by an independent safety review committee, and the national regulators.”

“All routine follow-up appointments continued as normal during this period,” they said.

“We are committed to the safety of our participants and the highest standards of conduct in our studies and will continue to monitor safety closely.”