A COVID-19 vaccine that Australia has ordered 10 million doses of was more than 90 per cent effective in stopping people from becoming infected, trials show.

The US pharmaceutical giant Pfizer, which developed the experimental vaccine with German immunotherapy company BioNTech, has released successful data from the final stage of its clinical trial.

It showed their mRNA-based vaccine “can help prevent COVID-19 in the majority of people who receive it”, Pfizer chair and chief executive Albert Bourla said in a statement.

He said early results from a large-scale Phase 3 study revealed the vaccine candidate was “more than 90 per cent effective in preventing COVID-19 in participants without evidence of prior SARS-CoV-2 infection”.

The breakthrough offers global hope at a time when the virus is running rampant in the USA and across Europe, with record daily infections.

America’s top infectious diseases expert Dr Anthony Fauci said the results were “just extraordinary”.

Tweet from @pfizer

The interim analysis was conducted after 94 participants in the trial developed COVID-19, examining how many of them had received the vaccine versus a placebo.

Over 90 per cent effectiveness implies that no more than 8 of the 94 people who caught COVID-19 had been given the vaccine, which was administered in two shots about three weeks apart.

The efficacy rate is well above the 50 per cent effectiveness required by the US Food and Drug Administration and for a coronavirus vaccine.

“We are one step closer to potentially providing people around the world with a much-needed breakthrough to help bring an end to this global pandemic,” Mr Bourla said.

The data has yet to be peer-reviewed or published in a medical journal.

The World Health Organisation chief Tedros Adhanom Ghebreyesus said the early results were “encouraging”.

Tweet from @DrTedros

Senior WHO official Bruce Aylward said the interim results were “very positive” and a vaccine may be rolled out by March 2021 to the most vulnerable.

“There is still much work to be done, this is just interim results…but some very positive results coming today which should hold great promise hopefully for the entire world as we move forward,” Mr Aylward told WHO’s annual ministerial assembly.

“By March as a result of the extraordinary work happening globally we could be in a position to fundamentally change the direction and the dynamic of this crisis,” he added.

Pfizer and BioNTech will submit an application to the US Food and Drug Administration in the third week of November when it will have enough safety data for emergency use authorisation of the vaccine.

“Even if that is achieved and some Americans are vaccinated later this year, it will be many more months before there is widespread vaccination in this country,” President-elect Joe Biden said in a statement.

He said the news was excellent but did not change the fact that face masks, social distancing and other health measures would be needed well into next year.

US President Donald Trump welcomed the test results, and the market boost: “STOCK MARKET UP BIG, VACCINE COMING SOON. REPORT 90% EFFECTIVE. SUCH GREAT NEWS!” he said on Twitter.

Pfizer and BioNTech said they had so far found no serious safety concerns.

Prime Minister Scott Morrison has said the Government’s COVID-19 Vaccine and Treatment Strategy had secured access to 10 million doses of the Pfizer BioNTech vaccine.

If it is proven to be safe and effective, its vaccine is expected to become available in Australia from early to mid-2021.

In such a scenario, five million Australians will get this vaccine given everyone will need to get two jabs.

A separate company called Novavax will supply another 40 million vaccine doses in Australia if that, too, is proven to be safe and effective.

Health experts said Pfizer’s results were positive for all COVID-19 vaccines currently in development.

Pfizer has forgone its traditional secrecy during the coronavirus vaccine trials. Photo: AAP

Mr Bourla said they showed the shots were going after the right target and proof the disease could be halted with vaccination.

“Today is a great day for science and humanity,” he said.

“We are reaching this critical milestone in our vaccine development program at a time when the world needs it most with infection rates setting new records, hospitals nearing over-capacity and economies struggling to reopen.”

BioNTech Chief Executive Ugur Sahin told Reuters he was optimistic the immunisation effect of the vaccine would last for a year although that was not certain yet.

“This news made me smile from ear to ear. It is a relief to see such positive results on this vaccine and bodes well for COVID-19 vaccines in general,” said Peter Horby, professor of emerging infectious diseases at the University of Oxford.

“The efficacy data are really impressive. This is better than most of us anticipated,” said William Schaffner, infectious diseases expert at Vanderbilt University School of Medicine, Nashville, Tennessee.

“The study isn’t completed yet but nonetheless the data look very solid.”

Pfizer said it expected to produce up to 1.3 billion doses of the vaccine in 2021.

“I’m near ecstatic,” Bill Gruber, one of Pfizer’s top vaccine scientists, said in an interview.

“This is a great day for public health and for the potential to get us all out of the circumstances we’re now in.”

-with AAP