"A COVID-19 vaccine will not be made available to Australians until it passes the strict safety and efficacious regulatory assessments by the Therapeutic Goods Administration (TGA)," Health Minister Greg Hunt said in a statement on Wednesday.

Pharmaceutical company AstraZeneca announced the trial had been paused to review an adverse reaction to the vaccine that was experienced by a participant in the trial in the United Kingdom.

No details of the adverse reaction have been released.

"The TGA rigorously assesses vaccines for safety, quality and effectiveness, before they can be legally supplied in Australia," Mr Hunt said.

"The TGA is actively monitoring COVID-19 vaccine development, including safety information, both in Australia and around the world."

On Monday the federal government announced the details of the deal it had signed with AstraZeneca and Australian company CSL, for CSL to manufacture millions of doses of vaccines if the Oxford University candidate, and another in development at the University of Queensland, successfully pass the clinical trials.

"The Australian government is in discussions with a number of other promising vaccines and will consider further investments in line with Australia's COVID-19 Vaccine and Treatment Strategy," Mr Hunt said.

Deputy chief medical officer Nick Coatsworth said it was "quite normal" for a pause in a clinical trial to investigate an adverse reaction, and that a review could take just a few days.

"We are not able to speculate on the effect of this particular pause because we simply don't have enough information at the moment," he said

Vaccines and other medications go through a series of clinical trials to ensure they are both safe and effective, with the number of people tested growing at each phase. Under the current phase three trial for the AstraZeneca vaccine, 50,000 people are being injected with the vaccine candidate.

A spokesperson for AstraZeneca said on Wednesday the trial was paused when the standard review process was triggered.

"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 spokesperson said.

"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 standards of conduct in our trials."

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