The coronavirus vaccine being developed by Pfizer and BioNTech has been found to be 90% effective in preventing people from getting the virus, it has been confirmed.
Phase 3 of Pfizer's trial involved 43,538 participants. They received two doses of either the immunisation or a placebo, with 90% protected from the virus within 28 days of having their jabs.
Only 94 people who took part in the trial developed coronavirus and no serious safety concerns were reported, the US pharmaceutical firm said on Monday.
"Today is a great day for science and humanity. The first set of results from our Phase 3 COVID-19 vaccine trial provides the initial evidence of our vaccine's ability to prevent COVID-19," said Pfizer chairman and chief executive Dr Albert Bourla.
"With today's news, we are a significant step closer to providing people around the world with a much-needed breakthrough to help bring an end to this global health crisis.
"While we are all in the midst of a second wave and many of us in lockdown, we appreciate even more how important this milestone is on our path towards ending this pandemic and for all of us to regain a sense of normality," he added.
Pfizer and BioNTech's vaccine is one of around 12 around the world that are in the final stages of testing.
The two companies say they can supply 50 million doses by the end of 2020 and 1.3 billion by the end of 2021.
The UK government has secured around 100 million doses in an agreement with the two firms.
Sky News science correspondent Thomas Moore said the results "exceed the expectations of many scientists".
Peter Horby, professor of emerging diseases and global health at the University of Oxford described the development as a "watershed moment".
He said: "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."
Michael Head, senior research fellow in global health at the University of Southampton, commented: "This cautiously sounds like an excellent result from the Phase 3, but we should remain a little cautious - the study is ongoing.
"However, if the final results show an effectiveness of anywhere near 90% with response in elderly and
ethnic minority populations, that is an excellent result for a first generation vaccine."
William Schaffner, infectious disease expert at Vanderbilt University Medical Center in Nashville, Tennessee, added: "The efficacy data is really impressive.
"This is better than most of us anticipated. I would have been delighted with efficacy of 70% or 75%, 90% is very impressive for any vaccine. The study isn't completed yet, but nonetheless the data looks very solid."