A huge study of another COVID-19 vaccine candidate is getting underway Monday as states in the US continue to roll out scarce supplies of the nation’s first shot options.

The US has authorized emergency use of two vaccines, one made by Pfizer and BioNTech and the other by Moderna, but doses will be rationed for months.

The candidate made by Novavax Inc. is the fifth to reach final-stage testing in the US Some 30,000 volunteers are needed to prove if this vaccine – a different kind than its Pfizer and Moderna competitors – really works and is safe.

The study, which is funded by the US government, is open to all adults but will focus on high-risk older adults and volunteers from Black and Hispanic communities who have been hard-hit 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.