Mortality burden of the 1918–1919 influenza pandemic in Europe

BACKGROUND: The origin and estimated death toll of the 1918-1919 epidemic are still debated. Europe, one of the candidate sites for pandemic emergence, has detailed pandemic mortality information. OBJECTIVE: To determine the mortality impact of the 1918 pandemic in 14 European countries, accounting for approximately three-quarters of the European population (250 million in 1918). METHODS: We analyzed monthly all-cause civilian mortality rates in the 14 countries, accounting for approximately three-quarters of the European population (250 million in 1918). A periodic regression model was applied to estimate excess mortality from 1906 to 1922. Using the 1906-1917 data as a training set, the method provided a non-epidemic baseline for 1918-1922. Excess mortality was the mortality observed above this baseline. It represents the upper bound of the mortality attributable to the flu pandemic. RESULTS: Our analysis suggests that 2.64 million excess deaths occurred in Europe during the period when Spanish flu was circulating. The method provided space variation of the excess mortality: the highest and lowest cumulative excess/predicted mortality ratios were observed in Italy (+172%) and Finland (+33%). Excess-death curves showed high synchrony in 1918-1919 with peak mortality occurring in all countries during a 2-month window (Oct-Nov 1918). CONCLUSIONS: During the Spanish flu, the excess mortality was 1.1% of the European population. Our study highlights the synchrony of the mortality waves in the different countries, which pleads against a European origin of the pandemic, as was sometimes hypothesized.