Pfizer expects to seek broad US emergency use authorisation of the vaccine for people aged 16 to 85. To do so,it will need to have collected two months of safety data on around half of the study's roughly 44,000 participants,expected in late November.

"I'm near ecstatic,"Bill Gruber,one of Pfizer's top vaccine scientists,said."This is a great day for public health and for the potential to get us all out of the circumstances we're now in."

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

The company did not break down exactly how many of those who fell ill received the vaccine. Still,more than 90 per cent effectiveness implies that no more than eight 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 for a coronavirus vaccine.

To confirm its efficacy rate,Pfizer said it will continue the trial until there are 164 COVID-19 cases among participants. Given the recent spike in US infection rates,that number could be reached by early December,Gruber said.

The data is yet to be peer-reviewed or published in a medical journal. Pfizer said it would do so once it has results from the entire trial.

Pfizer and BioNTech have a $US1.95 billion ($2.67 billion) contract with the US government to deliver 100 million vaccine doses beginning this year. They have also reached supply agreements with the European Union,the UK,Canada and Japan.

Under the new deal with the Australian government,Pfizer/BioNTech will provide 10 million doses should the vaccines be proven safe and effective through advanced clinical trials.

Prime Minister Scott Morrison said by securing multiple agreements,the government was giving Australians the best shot at early access to a vaccine,should trials prove successful.

"We aren't putting all our eggs in one basket and we will continue to pursue further vaccines should our medical experts recommend them,"Mr Morrison said.

"There are no guarantees that these vaccines will prove successful,however our strategy puts Australia at the front of the queue,if our medical experts give the vaccines the green light."

To save time,the companies began manufacturing the vaccine before they knew whether it would be effective. They now expect to produce up to 50 million doses or enough vaccine to protect 25 million people this year.

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

Reuters