With so much news about the Delta variant and calls for many vaccinated people to mask up again, Gigi Gronvall of the Johns Hopkins Center for Health Security talks with Stephanie Desmon about what we know right now about breakthrough COVID-19 infections and how worried the vaccinated should be about getting sick from COVID-19. "The more people who get vaccinated, the fewer chances the virus that causes COVID-19 has to mutate into an even deadlier virus," Gronvall says.