By Julie Steenhuysen and Michael Erman

Nov 16 (Reuters) - Moderna Inc said on Monday its experimental vaccine was 94.5% effective in preventing COVID-19 based on interim data from a late-stage clinical trial, becoming the second U.S. company in a week to report results that far exceed expectations.

Together with Pfizer Inc's vaccine, also shown to be more than 90% effective, and pending more safety data and regulatory review, the United States could have two vaccines authorized for emergency use in December with as many as 60 million doses of vaccine available by the year's end.

Next year, the U.S. government could have access to more than 1 billion doses just from the two vaccine makers, more than needed for the country's 330 million residents.

The vaccines, both built using new technology known as messenger RNA or mRNA, represent powerful new tools to fight a pandemic that has infected 54 million people worldwide and killed 1.3 million. The news also comes at time when COVID-19 cases are soaring, hitting new records in the United States and pushing some European countries back into lockdowns.

"We are going to have a vaccine that can stop COVID-19," Moderna President Stephen Hoge said in a telephone interview.

Moderna's interim analysis was based on 95 infections among trial participants who received either a placebo or the vaccine. Of those, only five infections occurred in those who received the vaccine, which is administered in two shots 28 days apart.

A key advantage of Moderna's vaccine is that it does not need ultra-cold storage like Pfizer's, making it easier to distribute. Moderna expects it to be stable at standard refrigerator temperatures of 2 to 8 degrees Celsius (36 to 48°F) for 30 days and it can be stored for up to 6 months at -20 degrees Celsius.

Pfizer’s vaccine must be shipped and stored at minus 70 degrees Celsius, the sort of temperature typical of an Antarctic winter. At standard refrigerator temperatures, it can be stored for up to five days.

The data from Moderna's 30,000 participant-strong trial also showed the vaccine prevented cases of severe COVID-19, a question that still remains with the Pfizer vaccine. Of the 95 cases in Moderna's trial, 11 were severe and all 11 occurred among volunteers who got the placebo.

Moderna, part of the U.S. government's Operation Warp Speed program, expects to produce around 20 million doses of the vaccine for the United States this year, millions of which the company has already made, and is ready to ship if it receives FDA authorization.

"Assuming we get an emergency use authorization, we'll be ready to ship through Warp Speed almost in hours," Hoge said. "So it could start being distributed instantly."