A more traditional kind of COVID-19 vaccine has moved a step closer to the U.S. market.

Advisers to the Food and Drug Administration voted Tuesday to back shots made by Novavax for U.S. adults. If the FDA and CDC ultimately agree, Novavax's option could become the nation's fourth COVID-19 vaccine.

It's a protein vaccine, made with a more conventional technology than the Pfizer and Moderna shots, which used mRNA technology.

"We believe our vaccine offers a differentiated option built on a well-understood protein-based vaccine platform that can be an alternative to the portfolio of available vaccines to help fight the COVID-19 pandemic," Stanley C. Erck, president and CEO of Novavax, said when initially seeking authorization in the U.S.

In clinical trials, the company said its two-dose vaccine showed about a 90% efficacy against COVID-19. However, those trials were conducted prior to the omicron variant becoming the dominant strain.

Novavax said the most common side effects were headache, nausea, injection site tenderness and fatigue.

The Novavax vaccine is currently offered in other countries around the world.