In the past one hundred years, a medical miracle occurred in the United States. Death in Childhood Is No Longer Expected. Health progress in the 20th century resulted from the conquest of infectious diseases, often by environmental means or through preventive or therapeutic measures such as vaccines and antibiotics. In addition, sanitation and hygiene greatly assisted age longevity of the US population. In 2000, the population is older. An increasing proportion of the population is now older than 65 years. Life expectancy at birth increased by more than 25 years since 1900. Dramatic declines in morbidity occurred for the nine vaccine-preventable diseases for which vaccination was universally recommended for use in children before 1990 (excluding hepatitis B, rotavirus, and varicella). Morbidity associated with smallpox and polio caused by wild-type viruses declined 100% and nearly 100% for the other seven diseases.