Determinants of Influenza Excess Mortality in Sweden, 1910-1930

Jonas Helgertz, University of Minnesota/Lund University
Tommy Bengtsson, Lund University
Martin Dribe, Lund University

We use monthly mortality data for Sweden over the time period 1910-1930, covering the Spanish flu pandemic in addition to several well-defined influenza epidemics occurring during this period. Using individual level all-cause mortality data aggregated to the city/town/parish level (N=2,401), combined with aggregated monthly data on cause-specific morbidity and mortality, we identify four separate influenza outbreaks during this period. Besides the Spanish flu pandemic during the fall-winter and spring of 1918-1919, again resurging in the winter and spring of 1919-1920, Sweden experienced outbreaks associated with significantly elevated mortality during 1914-1915, 1922, and 1927. Our aim is to contribute to a better understanding about what made the 1918-1919 outbreak so unique. While it is well known that its devastatingly high mortality largely is attributable to a shift in the typical age-mortality pattern, in this paper we investigate the role of a range of contextual factors expected to be important for the spread of an airborne infectious disease like the influenza, not only for all age and age-specific excess mortality during the main 1918-1919 wave of the Spanish flu, but for all influenza outbreaks occurring in Sweden during the period 1910-1930. In doing do, we aim to further illustrate what made the Spanish flu so unique and unpredictable, by being able to compare with outbreaks that were characterized by features more consistent with recurring epidemic influenza outbreaks. Lastly, we investigate interdependencies between the influenza outbreaks, in order to investigate signs of acquired immunity.

No extended abstract or paper available

 Presented in Session 150. Environmental and Social Dimensions of Infectious Disease Mortality: Historical Perspectives