Fresh hopes for an effective vaccine on Monday (November 16).
Moderna says its experimental shot is 94.5% effective in preventing COVID-19.
That's based on interim data from a late-stage clinical trial.
It makes it the second U.S. company to report results that far exceed expectations.
Together with the Pfizer vaccine, and pending more safety data and regulatory review, the U.S. could have two vaccines authorised for emergency use by December.
A key advantage of Moderna's vaccine is that it does not need ultra-cold storage like Pfizer's, making it easier to distribute.
Production of the Moderna shots will partially be carried out by Swiss biotechnology firm Lonza at plants in the U.S. and Switzerland.
The news sent Moderna shares up around 17 percent.
Also on Monday, Russia said it expects to produce primarily freeze-dried Sputnik V coronavirus vaccine doses by the spring.
That would eliminate the need for transport at ultra-low temperatures.
Russia has an ambitious plan to inoculate its population.
But vaccine developers globally are scrambling to work out how to ship and store their vials, some of which must be kept in specialised freezers at extremely low temperatures.
The logistical challenge was brought into sharp focus after promising interim trial data for the vaccine developed by BioNTech and Pfizer.
It's been considered a major breakthrough in the race to curb the pandemic.
But it needs to be shipped and stored at minus 70 degrees Celsius, equivalent to an Antarctic winter.
That poses a challenge for even the most sophisticated hospitals.
For the moment, it also puts it out of reach for many poorer countries.