Novavax on Wednesday received Food and Drug Administration authorization for a booster dose of its COVID-19 vaccine.

Yet unlike the bivalent mRNA vaccines currently on the market, Novavax’s booster only targets the original strain of the virus, rather than the original strain and the omicron BA.4/BA.5 subvariants.

The company is studying an omicron-specific vaccine, but executives have said they think the current vaccine provides durable protection across different variants of the virus.

Last week, the company said its clinical trial showed a single booster dose given 8 to 11 months after a Novavax primary series resulted in increased antibodies against omicron BA.1, BA.2 and the dominant BA.5 subvariant.

The booster was authorized for adults aged 18 and older who can’t take an mRNA vaccine or don’t have access to one, as well as for adults who would otherwise not receive a booster, the company said.

The booster dose is meant to be given at least six months after completion of primary vaccination with any authorized or approved COVID-19 vaccine.

Previously, the Novavax vaccine was used only as a two-dose primary series, given three weeks apart. The new authorization could help increase lagging booster numbers. According to the Centers for Disease Control and Prevention (CDC), only 33 percent of the population has received a booster dose of COVID-19 vaccine.   

“The U.S. now has access to the Novavax COVID-19 Vaccine, Adjuvanted, the first protein-based option, as a booster,” Stanley C. Erck, Novavax president and CEO said in a statement. “According to CDC data, almost 50 percent of adults who received their primary series have yet to receive their first booster dose. Offering another vaccine choice may help increase COVID-19 booster vaccination rates for these adults.”

Unlike Pfizer and Moderna, Novavax relies on more traditional vaccine technology, similar to those used to protect against flu and for routine childhood immunizations against whooping cough and meningitis. 

The two-dose vaccine can be stored at normal refrigerator temperatures, making it easier to ship and use. 

While Novavax missed out on the initial wave of COVID-19 vaccinations, company executives said they were always banking on using it as a booster shot.

Once the CDC also signs off, vaccination can begin.