Widespread Vaccination and Historical Increases in Life Expectancy
As a recent ScienceDaily release points out - if we ignore the cries for more public funding in the guise of general doom and gloom regarding the current state of medicine - vaccination has had an enormous effect on health and prevalence of chronic disease in the time since its development:
A comprehensive system of vaccine development in the U.S. resulted in a reduction of 87 to more than 99 percent in illness from ten vaccine-preventable diseases during the twentieth century....
In addition to the major reductions in illness during the twentieth century from smallpox, diphtheria, measles, mumps, pertussis, polio, rubella, congenital rubella syndrome, tetanus, and H. influenzae, type b (in children less than 5 years old), new vaccines in the past 10 years for varicella (chickenpox), hepatitis A, and pneumococcal disease have led to significant reductions in disease in young children, including a drop of 92 percent in mortality from chickenpox in children four years and younger.
Quite aside from mortality rates and their effect on life expectancy, less chronic disease means less cellular and other forms of biochemical damage accumulated over a lifetime - and thus, by the Reliability Theory of aging, a better chance at a longer, healthier life. This class of explanation for historical gains in life span is explored elsewhere at Fight Aging!, so feel free to take a look. You might find some related musings on the fight against infectious disease interesting as well.