Northwestern University Professor of Infectious Diseases Dr. Michael Ison on what’s causing this flu epidemic

Ana Martinez, a medical assistant at the Sea Mar Community Health Center, gives a patient a flu shot, Thursday, Jan. 11, 2018 in Seattle. According to an update by the Centers for Disease Control and Prevention released Friday, Jan. 12, 2018, flu is now widespread in every state except Hawaii, but the good news is the flu season appears to be peaking. (AP Photo/Ted S. Warren)

Dr. Michael Ison of Northwestern University joins John to tell him what’s causing an exceptionally bad flu season, or epidemic. And, he tells you how effective a flu shot is this far into the cold and flu season.