Pfizer says its experimental Covid-19 vaccine is more than 90 per cent effective, a major victory in the fight against a pandemic that has killed more than a million people.
Pfizer and German partner BioNTech SE are the first drug makers to release successful data from a large-scale clinical trial of a coronavirus vaccine.
The companies said they have so far found no serious safety concerns and expect to seek US authorisation this month for emergency use of the vaccine.
Health experts said Pfizer's results were positive for all Covid-19 vaccines currently in development since they show the shots are going after the right target and are a proof of concept that the disease can be halted with vaccination.
"Today is a great day for science and humanity," Albert Bourla, Pfizer's chairman and chief executive, 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."
If Pfizer's vaccine is authorised, the number of doses will initially be limited and many questions remain, including how long the vaccine will provide protection.
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 prospect of a vaccine electrified world markets with S&P 500 futures hitting a record high and tourism and travel shares surging.
"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."
New Zealand's Research, Science and Innovation Minister Megan Woods said the progress was encouraging news, and if all went according to plan some doses could be delivered to New Zealand early next year.
New Zealand has signed a deal to buy 1.5 million vaccines, enough for 750,000 people, subject to it passing all clinical trials and being approved by Medsafe.
Woods said Medsafe would assess any vaccines as quickly as possible after being provided data from Pfizer.
Epidemiologist Professor Nick Wilson said while the development looked like good news, he wanted to wait until there was a peer-reviewed journal article which covered both effectiveness and safety.
US President-elect Joe Biden 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.
UK Prime Minister Boris Johnson said Britain was ready to roll out a mass Covid-19 vaccination programme but it was too early to rely on a vaccine as a solution to the coronavirus pandemic.
"I must stress that these are very, very early days, and we've talked for a long time, right about the distant bugle of the scientific cavalry coming over the brow of the hill," Johnson told a media conference after Pfizer's announcement.
"I can tell you that tonight that today that toot, that bugle is louder, but it's still some way off. We absolutely cannot rely on this news, as a solution."
Pfizer expects to seek broad US authorisation for emergency use of the vaccine for people aged 16 to 85.
To do so, it will need two months of safety data from about half the study's 44,000 participants, which is expected late this month.
"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."
Pfizer and BioNTech have a $US1.95 billion contract with the US government to deliver 100 million vaccine doses beginning this year.
They have also reached supply agreements with Australia, the European Union, the United Kingdom, Canada and Japan.
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 to protect 25 million people this year.
Pfizer said it expects to produce up to 1.3 billion doses of the vaccine in 2021.
The US pharmaceutical giant said 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.
The company did not break down exactly how many of those who fell ill received the vaccine.
Still, 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 for a coronavirus vaccine.
To confirm the efficacy rate, Pfizer said it would continue the trial until there are 164 Covid-19 cases among participants.
Bourla told CNBC on Monday that based on rising infection rates, the trial could be completed before the end of November.
The data have yet to be peer-reviewed or published in a medical journal.
"These are interesting first signals, but again they are only communicated in press releases," said Marylyn Addo, head of tropical medicine at the University Medical Center Hamburg-Eppendorf in Germany.
"Primary data are not yet available and a peer-reviewed publication is still pending. We still have to wait for the exact data before we can make a final assessment."
- Reuters / RNZ