Vaccines are among the most effective inventions in medical history. The twentieth century saw the successful introduction of vaccines against diphtheria, measles, mumps, and rubella, diseases that were once major killers in developed countries. Through the use of vaccines, smallpox was eradicated and polio and measles are close to being eliminated.
Vaccines are also among the most cost-effective tools in public health. Many infectious diseases can be prevented by vaccines that cost just a few dollars per child. The immune protection conferred by vaccines can last for a lifetime.