The Covid-19 vaccine Australia has invested in has been dealt a major setback after researchers uncovered a suspected serious adverse reaction in a trial participant.
The vaccine, being developed by pharmaceutical giant AstraZeneca and the University of Oxford, is being tested at dozens of sites around the world.
The stage three trial — the final part before safety and efficacy data can be submitted to regulators for approval — has tens of thousands of participants.
The adverse reaction — which AstraZeneca says is an unexplained illness — is believed to have affected a single participant in the UK.
A suspected "serious adverse reaction" means the participant may require hospitalisation. It could result in a life-threatening illness or even death.
Australia has ordered 84 million doses of the AstraZeneca vaccine to be rolled out next year. The federal Government has secured agreement with that vaccine along with at candidate as part of a A$1.7 billion supply and production agreement.
Deputy Chief Medical Officer Dr Nick Coatsworth said reports of a major setback in trials needed to be investigated.
Coatsworth told Today the reported adverse reaction in trials did "not mean that the Oxford vaccine is dead".
"But it is a serious adverse reaction, and it needs to be investigated," he said.
Coatsworth said it showed the Oxford vaccine developers were following rigorous safety procedures in reporting the incident.
"The focus on safety is exactly the same and I'm actually taking a lot of reassurance out of these early breaking stories this morning," he said. "It by no means it puts that vaccine completely off the table."
A spokesman for AstraZeneca, a frontrunner in the race for a Covid-19 vaccine, said in a statement that the company's "standard review process triggered a pause to vaccination to allow review of safety data."
According to medical news website Stat News, the nature of the adverse reaction and when it happened were also not known, though the participant is expected to recover.
An AstraZeneca spokesman said the trial pause was done out an "an abundance of caution."
He described the pause as "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."
He also said that the company is "working to expedite the review of the single event to minimise any potential impact on the trial timeline."
Researchers have noticed side effects from the vaccine before, but they have been listed as mild or moderate.
A phase one/two study published in July reported that about 60 per cent of 1000 participants given the vaccine experienced side effects.
All of the side effects, which included fever, headaches, muscle pain, and injection site reactions, were deemed mild or moderate. All of the side effects reported also subsided during the course of the study.
Trial holds are not uncommon, but it is a blow to worldwide hopes for a shot to be ready in the coming months, as the AstraZeneca shot was considered by many – including the World Health Organisation – to be the leading candidate worldwide.
Researchers had hoped to know whether the vaccine worked and was safe by year-end, but that now looks increasingly unlikely.
Market confidence in AstraZeneca took a hit as soon as reports of the trial hold emerged.
Shares for AstraZeneca plummeted by 8 per cent in after-hours trading.
Coatsworth told Sunrise the Australian Government is investing in multiple technologies, multiple candidates for a Covis vaccine.
"We know not all of them will go to market," he told Sunrise. "And that's why we have got so many different vaccines candidates, I believe over 160 around the world, that are being tested."