The World Health Organization (WHO) tells us that herd immunity is the indirect protection from an infectious disease that happens when a population is largely immune, preferably through vaccinations but also through previous infection.

You see, vaccines train our immune systems to create proteins that fight disease, known as antibodies, just as would happen when we are exposed to a disease. But – crucially – vaccines create immunity without causing illness or resulting complications. Vaccinated people are protected from getting the disease and passing on the pathogen, breaking any chains of transmission. Dr. Ben Stong visits with Mark Alyn on this edition of Late Night Health.