Excess Deaths during 1918–1920 Pandemic, Taiwan | CDC EID

EID Journal Home > Volume 15, Number 10–October 2009

Volume 15, Number 10–October 2009
Dispatch
Excess Deaths and Immunoprotection during 1918–1920 Influenza Pandemic, Taiwan
Ying-Hen Hsieh
Author affiliation: China Medical University, Taichung, Taiwan

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Abstract
To determine the difference in age-specific immunoprotection during waves of influenza epidemics, we analyzed excess monthly death data for the 1918–1920 influenza pandemic in Taiwan. For persons 10–19 years of age, percentage of excess deaths was lowest in 1918 and significantly higher in 1920, perhaps indicating lack of immunoprotection from the first wave.

Recent studies have focused on quantifying the global effects of the influenza pandemic of 1918–1920 (1–3). This pandemic swept through Taiwan in 2 waves, at the end of 1918 and again in early 1920, causing devastating loss of human life. A report about the devastation brought by the first wave of the influenza epidemic, published in February 1920 (4), indicated that as of December 15, 1918, a total of 779,522 persons (20.8% of the population) had been infected and 25,394 persons had died from influenza; case-fatality rate was 3.26% (4,5). Although the number of infections decreased dramatically in early 1919, a second wave of the epidemic at the end of that year created another severe death toll.

Previous studies have shown that excess deaths, similar to those noted in the temperate zones, were also observed in Taiwan, which is in a tropical–subtropical zone, during periods of previously recognized influenza epidemics (6,7). A recent study has also shown Taiwan to be an evolutionarily leading region for global circulation of influenza virus A (H3N2) (8). Therefore, we analyzed the 1918–1920 pandemic in Taiwan to contribute to understanding of and preparation for possible future pandemic events.

The Study
Using data from the 1895–1945 Statistical Abstract of Taiwan (9), we compared monthly deaths during the 2 waves of epidemics in 1918 and 1920 with deaths during corresponding nonpandemic periods of the adjacent years. For example, we compared monthly deaths for November and December 1918 with the mean deaths for November and December 1916–1917 and 1919–1922. Statistically significant excess deaths were computed by detecting the data points at which the all-cause deaths exceeded the mean of the adjacent years +2 SDs (6,10). Excess deaths, computed from the mean number of deaths at these data points, were then used to ascertain the effect of the pandemic on deaths during these periods. During 1918–1920, population data were divided into 3 major groups: Taiwanese (95.2%), Mainland Chinese (0.57%), and Japanese–Korean (4.2%). However, only records of all-cause deaths for Taiwanese and Japanese were available and used in our analysis.

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