Drugmaker AstraZeneca has paused the trial of a potential coronavirus vaccine developed by Oxford University over risks of a “potentially dangerous illness” stemming from the use of the treatment, NBC News reports.

The Oxford virus uses an adenovirus virus to depress the production of a protein the coronavirus manipulates to infect the human body.

“Our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee,” the company said in a statement. “This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials.”

“In large trials illnesses will happen by chance but must be independently reviewed to check this carefully,” the statement continues.  “We are working to expedite the review of the single event to minimize any potential impact on the trial timeline. We are committed to the safety of our participants and the highest standards of conduct in our trials.”

The AstraZeneca vaccine began Phase 3 clinical trials in the United States last week.  Pfizer and Moderna have had drugs in Phase 3 trials in the US since July.

President Trump has hinted that a coronavirus vaccine may be introduced in the United States by the end of October, in an attempt to boost support for his reelection campaign.  The potential for a vaccine being developed that quickly has met with skepticism from medical and scientific professionals as being politically motivated.