Grant: Operating Grant

The worldwide spread of a novel influenza A (H1N1) virus in 2009 reminds us that influenza still represents a significant threat to public health. As was the case during its famous predecessor in 1918, the H1N1 strain that circulated in 2009 primarily targeted age-groups that are usually spared by influenza: adolescents and young adults. This project attempts to solve the mystery of high young adult mortality during the Spanish flu pandemic of 1918. We hypothesize that exposure to a virulent strain of influenza during critical periods of development results in physiological impairments that increase the risk of death from pandemic influenza in later life. We also posit that developing specific antibodies to a given influenza strain in early life may actually subvert the immune system, thereby increasing the risk of death when the individual is infected by a novel strain in later life. We will test whether early life exposure to pandemic influenza in 1890 increased the risk of dying from influenza during the next pandemic of 1918. To do this, we will link exact ages at death from publicly available historical records for Ontario and Quebec to information contained in census and other records that describe each individual's socioeconomic and environmental conditions during exposure to influenza and in later life. Drawing on historical demographic data and taking advantage of the most recent advances in developmental biology and immunology, this project brings a novel and exciting alternative to commonly held views about the unusual age pattern of mortality in 1918. Such knowledge could substantially improve crisis management were a new virulent and similarly age-patterned outbreak of influenza to emerge again on the world stage.