Final tests of some COVID-19 vaccines to start next month

The first experimental COVID-19 vaccine in the U.S. is on track to begin a huge study next month to prove if it really can fend off the coronavirus, while hard-hit Brazil is testing a different shot from China.Where to do crucial, late-stage testing and how many volunteers are needed to roll up their sleeves are big worries for health officials as the virus spread starts tapering off in parts of the world.Moderna Inc. said Thursday the vaccine it is developing with the National Institutes of Hea