The AstraZeneca coronavirus vaccine trial, halted last week after an unexplained illness in one of the volunteers, will resume, the University of Oxford announced Saturday.
The university, which is developing the vaccine with AstraZeneca, did not say when the trial would resume. AstraZeneca said the trial will only resume in the United Kingdom, adding that it's working with health authorities across the world to determine when other trials can resume.
Before the pause, the company was testing its vaccine, dubbed the Oxford vaccine, in the United States as well as in the United Kingdom, Latin America, Asia, Europe and Africa.
The university said in a statement that some 18,000 individuals around the world have received study vaccines 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 statement added.
US National Institutes of Health Director Dr. Francis Collins told a Senate hearing Wednesday that pausing a trial was a standard precaution that is meant to ensure experimental vaccines don't cause serious reactions among participants.
"To have a clinical hold, as has been placed on AstraZeneca, as of yesterday, because of a single serious adverse event, is not at all unprecedented," Collins said at a hearing of the Senate Heath, Education, Labor and Pensions committee.
On Tuesday, AstraZeneca joined eight other companies in signing a pledge promising they would not seek premature government approval for any coronavirus vaccine. The companies promised to wait until they had adequate data showing any potential vaccine worked safely.
AstraZeneca did not provide any details on the issue that caused the trial to stop. While AstraZeneca didn't specify what the issue was, at the hearing on Wednesday Collins said the AstraZeneca hold was due to a "spinal cord problem."
On Wednesday, AstraZeneca issued a statement denying news reports that suggested the trial was stopped because of a case of transverse myelitis -- a rare inflammatory condition of the spinal cord. On the same day, AstraZeneca said it had paused its coronavirus vaccine trial not once but twice because of adverse events.
"We can also confirm that there was a brief trial pause in July while a safety review took place after one volunteer was confirmed to have an undiagnosed case of multiple sclerosis, which the independent panel concluded was unrelated to the vaccine," a company spokesperson said.
The AstraZeneca vaccine is one of three coronavirus vaccines in late-stage, Phase 3 trials in the US. It has the backing of the US federal government. Moderna and Pfizer/BioNTec are the other two groups with Phase 3 trials under way, also with federal government funding.