Diseases that were largely eradicated in the United States a generation ago-including whooping cough, measles, mumps-are returning, in part because nervous parents are skipping their children's shots. This NOVA special takes viewers around the world to track epidemics, explore the science behind vaccinations, and shed light on the risks of opting out. Highlighting real cases and placing them in historical context, the program traces outbreaks of communicable diseases and demonstrates just how fast they can spread-and how many people can fall sick-when a community's immunity barrier falls.

Encoded with permission by Infobase on November 22, 2014.

Intro to Vaccines: Calling the Shots --(2:11) -- Vaccine Debate -- (1:38) -- Pertussis -- (2:34) -- Measles Outbreak in Brooklyn, New York -- (3:59) -- Anthropology of the Vaccine -- (2:41) -- Why People Do Not Vaccinate -- (1:57) -- Early Inoculation and Fear -- (3:40) -- Understanding Immunity and Vaccination -- (3:57) -- Herd Immunity -- (2:25) -- Effect of Low Vaccination Rates -- (1:41) -- Dravet Syndrome -- (4:55) -- Oral Polio Vaccine -- (3:48) -- Autism Advocate -- (3:36) -- DNA Sequencing Technology -- (2:05) -- HPV Vaccine -- (3:01) -- Disease Prevention -- (3:13) -- Risk Versus Benefit -- (2:21) -- Future of Vaccines -- (2:18) -- Credits: Vaccines: Calling the Shots -- (1:12).