The US Food and Drug Administration on Wednesday authorised Novavax Inc's COVID-19 vaccine as a booster for adults, helping the company's shares reverse course and rise more than 3%.
The approval applies for people unable to get updated Omicron-tailored boosters, or those who would choose not to receive any other booster dose.
The US Centers for Disease Control and Prevention (CDC) will now have to recommend use of the vaccine as a booster.
Wednesday's decision is in addition to the earlier clearance for the protein-based vaccine as a primary two-shot regimen for those 12 years and above.
Novavax's vaccine is based on an older technology that has been used for decades to combat diseases including hepatitis B and influenza.
Government authorities hoped that the shot would find wider acceptance among vaccine skeptics who were unwilling to take shots from Pfizer and Moderna, who used the ground-breaking messenger RNA technology.
Novavax, however, has been struggling to boost sales of the vaccine and in August halved its full-year revenue forecast, saying it does not expect further sales of the shot in the United States this year.
Only around 35,000 doses of the vaccine have been administered across the United States so far since the company originally got the regulator's nod in July, as per CDC data.
However, over half the population in the United States eligible for booster is yet to take it, as per the data.
"Offering another vaccine choice may help increase COVID-19 booster vaccination rates for these adults," Novavax Chief Executive Officer Stanley Erck said in a statement.