Moderna's coronavirus vaccine on Friday became the second to receive emergency use authorisation (EUA) from the US Food and Drug Administration, welcome news to a nation with a staggering Covid-19 death toll of over 307,000 lives lost.
The FDA announced the authorisation the day after the agency's panel of outside experts endorsed its use.
"Congratulations, the Moderna vaccine is now available!" tweeted President Donald Trump.
The decision marks the first regulatory approval in the world for Moderna's vaccine and validation of its messenger RNA technology. It came less than a year after the first Covid-19 case was identified in the US.
The US is the first nation to authorize the two-dose regimen from Moderna, now the second vaccine to be deployed in a Western country after the first, developed by Pfizer and BioNTech.
The biotech company has worked with the US government to prepare for the distribution of 5.9 million shots as early as this weekend.
The FDA decision is based on results from a late-stage study of 30,000 volunteers that found the vaccine was nearly 95 per cent effective at preventing illness from Covid-19 with no serious safety concerns.
The authorisation follows an EUA granted for a similar vaccine from Pfizer and German partner BioNTech that has been put into the arms of thousands of US healthcare workers this week in a massive nationwide rollout.
"With the availability of two vaccines now for the prevention of Covid-19, the FDA has taken another crucial step in the fight against this global pandemic that is causing vast numbers of hospitalizations and deaths in the United States each day,” FDA Commissioner Stephen Hahn, said in a statement.
Moderna's shot is expected to be used in harder-to-reach locations, such as rural hospitals. The vaccine needs to be stored and shipped frozen, but does not require the ultra-cold temperatures of the Pfizer-BioNTech shot.
Once thawed, the Moderna vaccine can be kept at typical refrigerator temperatures. It is administered in two shots 28 days apart.
Moderna has deals with the US government to provide 20 million doses this year and a total of 200 million doses by the end of June 2021.