A vaccine review panel has recommended that the Food and Drug Administration issue a second emergency use authorisation for the Covid-19 vaccine made by Moderna.
The panel members voted 20-0 in approval, with one abstention.
They believed the vaccine is safe enough for people over the age of 18 and that the benefits outweigh the risk for emergency use authorisation.
The panel held a day-long meeting to discuss safety, efficacy and other concerns before voting on the recommendation.
The move marks the huge scientific accomplishment of producing and gaining approval for two vaccines against a virus that was discovered only about a year ago.
It is expected that the full FDA will follow the panel's ruling and reports say the agency's approval could come as early as Friday.
After FDA approval, the Centres for Disease Control and Prevention will vote this weekend.
The vaccine can then be distributed to frontline healthcare workers and nursing home residents.
The FDA and the CDC approved emergency use of the Pfizer-BioNTech vaccine a week ago, making it the first Covid-19 vaccine approved in the US.
Immunisations started at the beginning of this week.
The vaccine is also being used in the UK, Canada, Saudi Arabia and other countries, and is awaiting approval for use in the EU.
The Moderna and Pfizer vaccines require two doses, although the Moderna vaccine can be stored in normal freezers and does not need to be moved in super-cold refrigerators like the Pfizer vaccine.
The company's vaccine was developed in collaboration with the National Institutes of Health.
The Pfizer-BioNTech vaccine was recommended for approval after the deadliest day in the US pandemic.
The Moderna vaccine was approved after more than 3,700 people died in the past 24 hours from Covid-19, Johns Hopkins University says.
More than 200,000 cases are recorded each day in the US and healthcare systems are reporting a record number of people with the virus in hospitals.
It is expected that holiday travel and gatherings for Christmas and the New Year will lead to further cases.
The US government has ordered 200 million doses from Moderna.
The company says it will try to make 50 million doses available for 25 million people before the end of December.