There are now more than 120 confirmed measles cases linked to an outbreak in western Texas, the largest such outbreak the state has seen in over 30 years. It's raising questions about vaccine hesitancy in some communities and the growing challenge of these periodic outbreaks. William Brangham discussed more with Caitlin Rivers, author of "Crisis Averted: The Hidden Science of Fighting Outbreaks." PBS News is supported by - https://www.pbs.org/newshour/about/funders