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 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 rose as much as 12% as of 2:52 p.m. in New York, their biggest intraday gain in almost a month. They had lost about a third of their value this year before today.

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.

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 has said it’s ready to ship 6 million doses to pharmacies and clinics throughout the US. “Our goal was always to be on the market when consumers and healthcare 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.