The US Centers for Disease Control and Prevention (CDC) on Tuesday recommended use of Novavax Inc's Covid-19 vaccine for individuals aged 18 and above.
CDC director Rochelle Walensky said the decision "expanded the options available" to US adults for vaccinations.
"If you have been waiting for a Covid-19 vaccine built on a different technology than those previously available, now is the time to join the millions of Americans who have been vaccinated," she said.
The recommendation came after the CDC's Advisory Committee on Immunization Practices (ACIP) unanimously backed the shot, a week after the US Food and Drug Administration authorised the vaccine as two-dose primary vaccination series.
The US government has secured 3.2 million Novavax vaccine doses. Novavax said in an emailed statement that it expects to ship doses for the US government to distribute in the coming days.
More than 77% of US adults have been fully vaccinated with shots from Moderna Inc, Pfizer-BioNTech, or Johnson & Johnson.
Novavax hopes its protein-based shot can reach wider acceptance among vaccine sceptics, because it uses an older technology than the messenger RNA vaccines. Protein-based vaccines have been used for decades to combat diseases including hepatitis B and influenza.
With the Novavax shots, "we really need to focus on that population with the hope that (the new shot) will change them over from being unvaccinated," Dr Oliver Brooks, one of the ACIP voting members said.
In a 30,000 participant clinical trial conducted before the emergence of the vaccine-evasive Omicron variant, the two-dose vaccine was around 90% effective at preventing illness from Covid.
In July, Novavax said the vaccine shows broad immune response to currently circulating variants, including Omicron subvariants BA.4/5.
Serum Institute of India, company's manufacturing partner, received FDA approval last week to export the vaccine to the country.
The Novavax shot has been available in Europe since December, but there has not been significant demand for it there. More than 13 million doses of the vaccine have been distributed around the EU, but only around 250,000 doses of the vaccine have been administered there.
Last week, the European Medicines Agency identified severe allergic reactions as potential side effects of the shot while the US product label warns against administering the shot to people with a history of allergic reactions to any components of the shot.
Novavax has been testing updated vaccine based on the first BA.1 Omicron variant and expects it to be available by the fourth quarter.
The company has also accelerated development of shots to protect against the BA.4 and BA.5 subvariants and expects additional preclinical data on such in late summer or fall.