According to the U.S. Census Bureau, the average life expectancy at the beginning of the 20th century was 47.3 years. A century later, that number had increased to 77.85 years, due largely to the development of vaccinations and other treatments for deadly diseases. Of course, vaccines and treatments only work if they're given, which is why many of these diseases still persist in poorer, developing countries. Despite the success of vaccines, only one of these diseases -- smallpox -- has been erased from the globe. Here are 12 diseases that could be completely eradicated from the world if vaccines were made available to all.

1. Chicken Pox

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).

Chicken pox, diphtheria, and polio are only a few of the devastating diseases that have been managed with vaccines in the 20th century.

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 do not 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.