Pfizer/BioNTech say final results show vaccine 95% effective
They said the two-dose vaccine had no serious safety concerns and that the companies will apply for emergency use authorization from US regulators "within days."
The announcement came as coronavirus cases are surging in the US and other parts of the world, and boosted hopes for an end to the pandemic that has upended life around the globe.
Pfizer has previously said it expected to contact the US Food and Drug Administration to apply for an Emergency Use Authorization by the third week of November.
The FDA had imposed a requirement on Covid-19 vaccine makers of having at least two months of follow-up with volunteers after their second dose, taken 28 days after the first, in order to ensure the drugs are safe.
Moderna developed its vaccine along with the US National Institutes for Health.
Both vaccines use mRNA (messenger ribonucleic acid) technology to deliver genetic material to the body that makes human cells create a protein from the virus.
This trains the immune system to be ready to attack if it encounters SARS-CoV-2.
Other vaccines that are in late-stage trials, such as one being developed by Johnson & Johnson and another by Oxford University and AstraZeneca, use modified viruses to deliver genetic material for the same purpose.
No mRNA vaccines have ever been approved, but Anthony Fauci, the United States' top infectious disease scientist, told AFP Tuesday the technology had now "established itself."