One of the world’s most promising vaccine trials has been paused after a participant suffered an adverse reaction.

UK drug company AstraZeneca has had to put the promising COVID-19 trial run through Oxford University on hold after one participant became ill.

It is not yet known if his illness is linked to the vaccine.

The company said the “voluntary pause” was standard practice.

“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.

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“In large trials illnesses will happen by chance but must be independently reviewed to check this carefully.”

The Australian Government last week announced it had signed a deal to secure over 83 million doses of COVID vaccines being tested through Oxford University and Queensland University.

About 33 million doses would be supplied through Oxford and AstraZeneca, and the other 50 million would be supplied by Queensland University and CSL – the drug company responsible for manufacturing the yearly flu vaccine.

Deputy Chief Medical Officer Dr Nick Coatsworth said despite the urgency around securing a vaccine, “safety is at the forefront of everybody’s mind”.

“You’ve got to keep in mind tens of thousands of people have received this Oxford vaccine,” he said on Sunrise.

“This is a testimony to the rigor and the safety focus people are putting on vaccine development.”

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Dr Coatsworth said the pause of the trial “by no means puts the vaccine completely off the vaccine”.

“But it is the reason why the Australian in Government is investing in multiple technologies, multiple vaccine candidates,” he said.

“We know not all of them will go to market… We’ve invested in several of the leading candidates.”

More Perth news and COVID-19 updates on SoPerth.com.au.