The Moderna vaccine is 94.5% effective against coronavirus, according to early data released Monday by the company, making it the second vaccine in the United States to have a stunningly high success rate.

"These are obviously very exciting results," said Dr. Anthony Fauci, the nation's top infectious disease doctor. "It's just as good as it gets -- 94.5% is truly outstanding."

Moderna heard its results on a call Sunday afternoon with members of the Data Safety and Monitoring Board, an independent panel analyzing Moderna's clinical trial data.

"It was one of the greatest moments in my life and my career. It is absolutely amazing to be able to develop this vaccine and see the ability to prevent symptomatic disease with such high efficacy," said Dr. Tal Zacks, Moderna's chief medical officer.

Vaccinations could begin in the second half of December, Fauci said. Vaccinations are expected to begin with high-risk groups and to be available for the rest of the population next spring.

Last week, Pfizer announced that early data show its vaccine is more than 90% effective against the disease.

In Moderna's trial, 15,000 study participants were given a placebo, which is a shot of saline that has no effect. Over several months, 90 of them developed Covid-19, with 11 developing severe forms of the disease.

Another 15,000 participants were given the vaccine, and only five of them developed Covid-19. None of the five became severely ill.

The company says its vaccine did not have any serious side effects. A small percentage of those who received it experienced symptoms such as body aches and headaches.

Moderna plans to apply to the US Food and Drug Administration for authorization of its vaccine soon after it accumulates more safety data later this month.

Fauci says he expects the first Covid-19 vaccinations to begin "towards the latter part of December, rather than the early part of December."

Initially, there won't be enough vaccine for everyone. The highest priority groups, which include health care workers, the elderly, and people with underlying medical conditions, will get the vaccine first.

"I think that everybody else will start to get vaccinated towards the end of April," Fauci said. "And that will go into May, June, July. It will take a couple of months to do."