Why another flu pandemic is likely just a matter of when

Despite the availability of vaccines, the flu still kills tens of thousands of people in the U.S. each year, and hundreds of thousands more worldwide. But public health officials fear that an even graver threat lies ahead: the emergence of a new, much more deadly flu virus. As William Brangham reports, the scenario has occurred before. Stream your PBS favorites with the PBS app: https://to.pbs.org/2Jb8twG Find more from PBS NewsHour at https://www.pbs.org/newshour Subscribe to our YouTube channel: https://bit.ly/2HfsCD6 Follow us: Facebook: http://www.pbs.org/newshour Twitter:   / newshour   Instagram:   / newshour   Snapchat: @pbsnews Subscribe: PBS NewsHour podcasts: https://www.pbs.org/newshour/podcasts Newsletters: https://www.pbs.org/newshour/subscribe