The “Spanish Flu” of 1918 was the deadliest pandemic in modern history. Widely cited figures on the global mortality burden range from 50 to 100 million deaths (Johnson and Mueller, 2002). This wide range is partly due to the sparse data for countries in Africa and Asia. Similarly, estimates of local mortality rates also show enormous variation between and within countries. What explains these differences? This question is surprisingly hard to answer since, to date, the factors influencing differential regional severity of the 1918 influenza pandemic have not been fully explored.
My research shed lights on this topic by using parish-level data for the south-western German Kingdom of Württemberg and focusing on the effects of poverty and air pollution on regional mortality differences. Both factors also received considerable attention during the COVID-19 pandemic. The analysis adds to the existing literature on the severity of the pandemic in urban areas with extensive evidence from predominantly small rural parishes (see also an earlier article of this blog on the impact of this epidemic on racial inequality here). The focus on smaller communities is important because previous findings indicate substantial differences in pandemic severity depending on the degree of urbanisation.
The Spanish Flu in Württemberg
The Kingdom of Württemberg was one of the four kingdoms of the German Empire and the third-largest after Prussia and Bavaria. The influenza pandemic of 1918 reached the south-western German kingdom at the end of World War I in June 1918, followed by a second, even more deadly wave in October 1918 and finally the third wave in the spring of 1919. The pandemic hit a population starved by the war and lacking about 14 percent of the male population of military-age due to the fighting. Combined with the censorship of the media, these circumstances could explain why the public perceived the pandemic as a minor problem.
However, official statistics show that the number of influenza deaths in 1918 increased by about 3,000 percent compared to the previous years: 7,263 people died of influenza in 1918. The actual pandemic mortality is probably higher, as this figure does not take into account influenza deaths among military personnel and cases misdiagnosed as pneumonia, for example.
I provide new estimates of excess mortality rates (i.e. number of deaths per 1,000 population that exceeds the mortality rate expected in a normal year) for the German Empire, both at the aggregate and regional level. The estimates range from 2.5 to 8.0 excess deaths per 1,000 inhabitants throughout the country. These enormous differences in regional excess mortality call for a careful analysis of underlying factors. In the following, I focus on the role of income and air pollution, since these are often considered important drivers of airborne illnesses.
The effect of income and air pollution on pandemic mortality
My analysis uses annual figures of all-age mortality for the totality of Württemberg parishes in the years 1914-1925. I combine these with extensive socio-economic information from various population and occupational censuses. For each parish, I observe the level of total taxable income in 1907 and calculate the average per capita income. In addition, I link these data to available information on the location of coal-fired power plants, a main source of air pollution in the early 20th century.
I perform a quantitative analysis to estimate the effects of poverty and air pollution on pandemic mortality. My approach compares changes in mortality rates in low-income (least polluted) parishes with changes in mortality rates in high-income (highly polluted) parishes. The average overall mortality rate in Württemberg parishes in the pandemic year 1918 was 15.8 deaths per 1,000 people, an increase in the mortality rate of 2.9 deaths, or 23 per cent, from the baseline year of 1917.
The figures below present 1) the annual mortality rate per 1,000 persons for parishes in Württemberg by pollution tercile, as measured by installed coal-fired capacity within 50 kilometres of the respective parish; and 2) the annual mortality rate by income tercile. The figures show that mortality rates develop largely in parallel over time, except in the pandemic year 1918.
Middle- and high-income parishes (classified by per capita taxable income) experienced a much smaller increase in mortality rates than low-income parishes. The increase in mortality rates in middle- and high-income parishes was lower by 1.3 and 0.9 deaths per 1 000 inhabitants, respectively. In addition, the increase in mortality rate from 1917 to 1918 was significantly higher in highly polluted parishes than in least polluted parishes. The estimates indicate an additional 1.6 deaths per 1,000 population increase in the mortality rate.
What explains the strong link between pollution and mortality? Several studies show its negative effects on susceptibility to respiratory diseases. For instance, air pollution causes oxidative stress in human respiratory cells and consequently increases the ability of the virus to enter these cells. The effects of income level differences on pandemic mortality are less well understood and require further investigation. However, these are associated with multiple factors that influence (pandemic) mortality, like the nutritional situation of individuals, access to sanitary infrastructure and healthcare, or housing conditions (see an earlier entry on the topic here). These differences in the general health situation could be amplified in a pandemic and cause an additional increase in mortality.
The regional impact of pandemics
My results show clearly that the increase in mortality in 1918 in Württemberg was particularly high in poor and highly polluted parishes. These findings are robust to a number of additional analyses. Overall, my research contributes to our understanding of regional differences in pandemic mortality and adds to the growing evidence of the harmful effects of regional income inequality and exposure to air pollution.
- Franke, R. (forthcoming). Poverty, Pollution, and Mortality: The 1918 Influenza Pandemic in a Developing German Economy. Economic History Review.
- Johnson, N. P. A. S. and Mueller, J. (2002). Updating the accounts: Global mortality of the 1918-1920 “Spanish” influenza pandemic. Bulletin of the History of Medicine, 76(1):105-115.
- Königliches Statistisches Landesamt (1910). Württembergische Gemeindestatistik. W. Kohlhammer Verlag, Stuttgart.
- Ott, H., Herzig, T., Allgeier, R., and Fehrenbach, P. (1981). Elektrizitätsversorgung von Baden, Württemberg und Hohenzollern 1913/14, chapter 11, 9. Historischer Atlas Baden-Württemberg.
- Statistisches Landesamt (1922). Württembergische Jahrbücher für Statistik und Landeskunde 1919/20. W. Kohlhammer, Stuttgart.
Postdoctoral researcher (University of Bayreuth)
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