The increased use of vaccination has led to a significant decrease or even to the disappearance of serious infectious diseases. Currently, vaccines are often evaluated by their potential side effects while ignoring the benefits. This happens because of memory loss. The memory of the damage caused by vaccine-preventable diseases has been lost. This paper illustrates the epidemiology of the major vaccine-preventable diseases and the risk of reintroduction of many pathologies in case the vaccine coverage continues to decrease.