AstraZeneca vaccine trial paused to investigate ‘a potentially unexplained illness’

One of the leading coronavirus vaccine clinical trials, from AstraZeneca, has been paused to investigate a “potentially unexplained illness” in one of the participants, the company said Tuesday.

The announcement could lead to a concerning setback to a high-profile coronavirus vaccine clinical trial, though much remains unknown, and it is not clear how much of an impediment the development will be.

“As part of the ongoing randomised, controlled global trials of the Oxford coronavirus vaccine, our standard review process triggered a pause to vaccination to allow review of safety data,” AstraZeneca 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.”

The statement said it is possible the illness in one of the participants in the trial is not even caused by the vaccine. “In large trials illnesses will happen by chance but must be independently reviewed to check this carefully,” the company said. “We are working to expedite the review of the single event to minimise any potential impact on the trial timeline.”

Stat, which first reported the pause in the trial, reported that the participant who had the “suspected serious adverse reaction” is in the United Kingdom.

AstraZeneca is one of three companies that have phase three coronavirus vaccine trials ongoing in the United States. Two other trials are being conducted for potential vaccines from Pfizer and Moderna.

This is the first time any of those three trials have been known to have been paused for a safety investigation.

The announcement illustrates the importance of a careful vaccine process to check safety and efficacy, and comes on the same day that AstraZeneca, as well as eight other drug companies, issued a rare joint statement pledging to follow the science and avoid politics, amid President Trump floating the idea of a pre-election approval of a vaccine. 

“We will need more information but obviously this is concerning,” tweeted Carlos del Rio, a vaccine expert at Emory University.