(Bloomberg) -- Novavax Inc.’s updated version of its Covid-19 shot gained US regulators’ authorization for emergency use amid a rocky rollout of competitors’ offerings.

The vaccine is authorized for use in people 12 and older, the Food and Drug Administration said Tuesday. “This adds a second technology option to the country’s public health arsenal to help protect individuals and their families against the XBB variant this fall,” Novavax said in a statement. The Centers for Disease Control and Prevention has included the shot among its recommendations, the company said. 

The authorization follows September approvals for boosters from Moderna Inc. and the partnership of Pfizer Inc. and BioNTech SE in the same age group. The messenger RNA shots from the companies were also authorized for emergency use in September for those aged six months and older. The Centers for Disease Control and Prevention has recommended that everyone who’s eligible should get a Covid booster. 

Shares of Novavax closed up 8.2% in New York. They had lost about a third of their value this year before Tuesday. 

Unlike the Pfizer and Moderna mRNA shots that teach cells to spark the creation of antibodies, Novavax’s stimulates the immune system with harmless versions of the spike protein that the virus uses to enter cells. All of the recent crop of boosters were formulated to protect against the XBB.1.5 strain of Covid, which accounted for around 40% of infections in June. 

Read More: Vaccine Breakthrough Behind Pfizer, Moderna Shots Wins Nobel 

Other variants including one called EG.5, or Eris, have since gained dominance over XBB.1.5. In August, Novavax said a study of animals indicated its vaccine was effective against the newer strain.  

Pharmacies have found themselves low on Moderna and Pfizer’s jabs, forcing them to turn people away who were seeking a booster shot during the first weeks it became available.

Novavax said Monday that it was ready to ship about 6 million doses to pharmacies and clinics throughout the US. On Tuesday, the company said that number fluctuates. 

“Our goal was always to be on the market when consumers and health-care providers were most concerned about getting people vaccinated, and we think the time is now,” Silvia Taylor, an executive vice president at Novavax, said in an interview.

(Updates with CDC recommendation in second paragraph.)

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