The US added a second COVID-19 vaccine to its arsenal on Friday after the Food and Drug Administration authorized an emergency rollout of Moderna's vaccine.
The move marks the world's first authorization for Moderna's shots. It comes as deaths per day in the country have hit all-time highs, eclipsing 3,600 on Wednesday. The virus has claimed more than 312,000 US lives. New cases are running at over 216,000 per day on average.
Moderna has about 5.9 million doses ready for shipment set to begin over the weekend.
In a study of 30,000 volunteers, the Moderna vaccine was more than 94% effective at preventing symptomatic COVID-19 in people 18 and older. It also strongly protected older adults, who are most vulnerable.
US President Donald Trump hailed the approval on Twitter.
"Today’s emergency use authorization by the Food & Drug Administration of the Moderna COVID-19 vaccine is another milestone in our battle to overcome the crisis our country is facing today," President-elect Joe Biden said in a statement.
Biden is due to receive the Pfizer-BioNTech vaccine publicly on Monday.
What's the difference between Moderna and Pfizer/BioNTech's vaccines?
Both shots are so-called mRNA vaccines, made with a groundbreaking new technology. They don't contain any coronavirus - meaning they cannot cause infection. Instead, they use a piece of genetic code that trains the immune system to recognize the spike protein on the surface of the virus, ready to attack if the real thing comes along.
Early results show both vaccines appear safe and strongly protective although Moderna's is easier to handle since it doesn't need to be stored at ultra-frozen temperatures.
Both the new Moderna vaccine and the Pfizer-BioNTech shot require two doses several weeks apart. The second dose must be from the same company as the first.
The inoculated can't throw away their masks as it's not yet clear either vaccine prevents silent, symptomless virus spread. But there was a hint that Moderna's shot might provide some protection against asymptomatic infection.
The Moderna study uncovered no major safety problems. Like with the Pfizer-BioNTech shot, expect sore arms, fever, fatigue and muscle aches, which are signs the immune system is revving up.
Both vaccines carry a "remote chance'' of causing a severe allergic reaction. Moderna's study turned up none of these, though a handful were reported in Britain as the Pfizer-BioNTech vaccinations got underway and the FDA is looking into five in the US.
Both vaccines remain experimental, and authorities are closely monitoring safety in case problems crop up.
Where do other countries stand in their vaccine strategies?
The FDA's decision could help pave the way for other countries that are considering the Moderna vaccine. European regulators could authorize its use as soon as January 6.
Moderna expects to have between 100 million and 125 million doses available globally in the first three months of 2021.
Britain, Canada and a few other countries already have cleared the Pfizer-BioNTech shot, with a European Union decision due Monday.