AstraZeneca has put on hold all global clinical trials of its Covid-19 vaccine candidate over a suspected adverse event in a study participant.

The vaccine, developed by the University of Oxford, is undergoing trials in multiple countries, including the UK, South Africa, Brazil and the US.

AstraZeneca said that it voluntarily paused the trials to facilitate review of safety data by an independent committee. The move comes after a participant in the UK trial experienced an unexplained illness.

The nature of the adverse reaction was not immediately known, but the participant is expected to recover, according to STAT News citing an individual familiar with the matter.

AstraZeneca noted that the pause was a routine action and the company is working to accelerate the review of the single event to reduce any impact on the trial timeline.

In a statement, the company said: “As part of the ongoing, randomised, controlled global trials of the Oxford coronavirus vaccine, our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee.

“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.”

In July this year, AstraZeneca reported positive data from the Phase I/II COV001 clinical trial of the Covid-19 vaccine, AZD1222.

Early data showed that the vaccine candidate was tolerated and generated strong immune responses in all evaluated participants. Findings have been published in The Lancet journal.

Last month, AstraZeneca launched a Phase III trial of the vaccine candidate in the US.