AstraZeneca pauses Covid-19 vaccine trial to review safety data

AstraZeneca paused the phase three clinical trial of the Covid-19 vaccine candidate that it was developing in conjunction with the University of Oxford, in response to a "potentially unexplained illness" in one of the participants.

The news was first reported by STAT News, which cited a company spokesperson according to whom a "standard review process triggered a pause to vaccination to allow review of safety data".

"In large trials, illnesses will happen by chance but must be independently reviewed to check this carefully," the spokesperson reportedly also explained.

The study was being conducted in 62 sites across the US, as well as in Brazil, Canada and the UK, with the participant experiencing the illness being located in the latter.

The nature of the adverse reaction and when it occurred remained unknown, as did the possible length of the company's decision to place the trial on hold.

However, AstraZeneca said that it was expediting the review of the "single event" so as to minimise its potential impact on the expected timeline for the trial.

One source cited by STAT News said the hold was decided upon out of an "abundance of caution", while a second source said that it was impacting other vaccine trials being conducted by AstraZeneca, because researchers outside the UK were now revising their data to search for any similar events.

STAT News nonetheless reported that the participant was expected to recover.

Trials being conducted by other pharmaceutical companies were also being impacted.

As of 0056 BST, American Depositary Receipts of AstraZeneca were trading 8.04% lower to $50.35.

Futures on the S&P 500 meanwhile were pointing 10.25 points lower to 3,325.25.