Prenatal Selection: Scarring Effects of Pandemic Influenza

Ogasawara, Kota

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. I find that fetal exposure to pandemic influenza during the first trimester of the pregnancy period decreases the proportion of males at birth during this period. The mechanism suggests that the decline in male births owing to pandemic influenza has not led to the positive selection into births, but it has been associated with the deterioration of fetal and infant health. This result supports a wide range of previous literature on the long-run adverse effects of pandemic influenza, and it is consistent with a recent argument that the postnatal selection mechanism owing to the socioeconomic status of parents is negligible (Almond 2006; Beach et al. 2018). Analyses using population censuses provide evidence suggesting that postnatal influenza exposure has long-term impacts on the sex ratio of children aged 5-12, thereby implying potential disturbance effects on the future marriage and labor markets.