For much of human history, infectious diseases were the main causes of morbidity and mortality. The sciences of public health, epidemiology, microbiology, and vaccine and drug development have dramatically reduced the risks associated with these diseases such that life expectancies in high income countries have increased by close to 40 years over the last century, principally due to a reduction in child deaths from infectious diseases. Today, chronic diseases are the main cause of mortality and are expected to increase over time.
