A huge U.S. study of another possible COVID-19 vaccine is getting underway as states continue to roll out scarce supplies of the first shots cleared for emergency use.
Doses of one vaccine made by Pfizer and BioNTech and another made by Moderna are rationed and more options are critical to amassing enough shots for the country and the world.
Novavax is recruiting 30,000 volunteers to test its shot, a different kind.
Still others are in the pipeline. Johnson & Johnson hopes to know next month if its one-dose option works. And Britain is considering green-lighting an AstraZeneca shot.