If it works, a vaccine would allow the world to return to some measure of normality after the tumult of the pandemic.

Both companies have contracts to provide vaccine to the United States and other governments if they are cleared by regulators.

An independent safety review conducted during what was referred to as a 'routine action' to maintain the 'integrity of the trials' ended Saturday.

A study participant in late-stage testing reported symptoms consistent with transverse myelitis, a rare inflammation of the spinal cord, said company spokesman Matthew Kent.

The World Health Organization (WHO) has flagged the AstraZeneca vaccine, which is being developed with the University of Oxford, as the most promising for coronavirus.

While it might be a setback, the researchers are ultimately being 'very careful,' according to one Canadian expert.

Oxford University has partnered with AstraZeneca, a British-Swedish multinational pharmaceutical and biopharmaceutical company, to produce 2 billion doses of the vaccine.

"Australia needs some hope," Prime Minister Scott Morrison said. "Today, we take another significant step to protect the health of Australians against the coronavirus pandemic."

As some countries proceed to human trials in the race for a COVID-19 vaccine, Canada lags behind with many questions left unanswered by federal officials.

Britain's AstraZeneca said on Thursday that good data was coming in so far on its vaccine for COVID-19, already in large-scale human trials and widely seen as the front-runner in the race for a shot against the virus.