“[Above] is a look at the past morbidity (how many people became sick) of what were once very common infectious diseases, and the current morbidity in the U.S. There’s no smallpox and no polio, almost no measles, dramatically less chickenpox (also known as varicella) and H. influenza (that’s not flu, but a bacteria that can cause deadly meningitis.”How Vaccines Have Changed Our World in One Graphic.