An important study of another COVID-19 vaccine candidate is under process as states in the U.S. continue to get scarce supplies of the nation’s first vaccine options.

The U.S. authority has approved the emergency use of two vaccines, one made by Pfizer and BioNTech and the other by Moderna, but doses will be available in lots for months.

The candidate made by Novavax Inc. is the fifth to reach final-stage testing in the U.S. The company needs over 30,000 volunteers to prove if this vaccine — a different kind than its Pfizer and Moderna competitors — is effective and is safe.

The study funded by the U.S. government is open to all adults but will focus on high-risk older adults and volunteers from Black and Hispanic communities who have been clobbered by the virus. Two-thirds of volunteers will receive the vaccine and the rest will get dummy shots.

The Novavax candidate uses lab-grown harmless copies of the spike protein that coats the coronavirus to train the body to recognize if the real virus comes along. The Pfizer and Moderna vaccines instead use a newer technology, injecting the genetic code for that protein.