World Immunization Week is the last week in April and this year's theme is The Big Catch Up. Vaccine expert Dr. Bill Moss returns to the podcast to talk with Dr. Josh Sharfstein about how major setbacks in global vaccine coverage over the past few years are seeding the deadly threat of a measles resurgence. They discuss contributing factors and what needs to be done to get out in front of one of the world's most infectious viruses.