Before 1995, a case of the chicken pox was a rite of passage for kids. The disease, caused by the varicella-zoster virus, creates an itchy rash of small red bumps on the skin. The virus spreads when someone who has the disease coughs or sneezes, and a nonimmune person inhales the viral particles. The virus can also be passed through contact with the fluid of chicken pox blisters. Most cases are minor but in more serious instances, chicken pox can trigger bacterial infections, viral pneumonia and encephalitis (inflammation of the brain).
According to the Centers for Disease Control and Prevention (CDC), before the chicken pox vaccine was approved for use in the United States in 1995, there were 11,000 hospitalizations and 100 deaths from the disease every year. Many countries don't require the vaccination because chicken pox doesn't cause that many deaths. They'd rather focus on vaccinating against the really serious diseases, so the disease is still common.
While chicken pox is still a relatively common occurrence, diseases like malaria and diphtheria seem to have been wiped out ages ago. Find out more about how these diseases were cured on the following pages.