Pandemic influenza and the gender imbalance: Evidence from early twentieth century Japan
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This study uses the 1918-1920 influenza pandemic in Japan with newly digitized and complete census records on births, infant deaths, and sex ratios during childhood to analyze mortality selection in utero and its persistency in the gender imbalance. We find that fetal exposure to pandemic influenza during the first trimester of the pregnancy period decreased the proportion of males at birth in this period. We then show that the decline in male births might have been associated with the deterioration of fetal health due to pandemic influenza. Analyses using Population Censuses provide suggestive evidence that fetal influenza exposure had long-term impacts on the sex ratio at 5-12 years old.
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