Routine vaccinations have made such an impact on public health that immunizations are considered one of the greatest medical achievements of the 20th century. Vaccines prevent disease in people who receive them and protect those who come in contact with unvaccinated individuals. Before vaccines, many children died from diseases such as polio. Through the introduction of routine vaccinations many diseases are becoming rare in the U.S. The viruses and bacteria that cause them still exist, though. Vaccinations are one of the best ways to put an end to the serious effects of certain diseases.