AstraZeneca and Oxford University halted the tests after a participant in the United Kingdom experienced a serious adverse reaction.

Australia has ordered 33 million doses of the AstraZeneca vaccine to be rolled out from early next year if the trials prove successful.

The federal government is hoping to gain early access to 3.8 million doses for distribution in January.

Deputy Chief Medical Officer Nick Coatsworth said the delay did not necessarily mean the vaccine deal was dead but the adverse reaction needed to be investigated.

He isn’t worried about the trial being put on hold and praised the transparency of those testing the vaccine.

“I’m going to wait to see exactly what the adverse reaction was and whether they attribute it to the vaccine,” Dr Coatsworth said on Wednesday.

AstraZeneca confirmed the trial had been voluntarily paused after an unexplained illness in a British participant.

An independent committee will now review the data.

“This is a routine action which has to happen whenever there is an unexplained illness in one of the trials, while it is investigated, ensuring we maintain the integrity of the trials,” the company said in a statement.

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

“We are working to expedite the review of the single event to minimise any potential impact on the trial timeline. We are committed to the safety of our participants and the highest standard of conduct in our trials.”

Earlier this week, Prime Minister Scott Morrison announced a $1.7 billion coronavirus vaccine deal.

Morrison promised to make two vaccines – the Oxford University and AstraZeneca drug, and another being developed by the University of Queensland and CSL – free for every Australian.

He said both vaccines would need to be proven safe and effective before being made available to the public.

-AAP