The Long Lasting Influenza: The Impact of Fetal Stress during the 1918 Influenza Pandemic on Socioeconomic Attainment and Health in Sweden 1968-2012

The observation in the 1940s, that children to mothers having rubella in the first part of the pregnancy experienced elevated health risks in later life led to a growing interest into whether fetal exposure to other – less severe – diseases could cause health problems as well. Epidemiological studies of the fetal origins of later life health that followed found that, while this indeed was the case, the effect was rather modest. A frequent weakness with many of these studies is furthermore that they only demonstrate associations, not causal relationships. Recent studies by economists and demographers, using quasi-experimental design to overcome this weakness, show that fetal conditions not only affect health in later life but also education and socioeconomic attainment. There is, however, a lack of consistency in the results. While some are showing strong effects, others show weak or no effects at all. Whether this is due to omitted variables, such as the socioeconomic status of parents or data quality problems is unclear. Thus, the question remains: does fetal stress caused by less severe diseases such as influenza, have long lasting impact on health and socioeconomic attainment? In this study we use a quasi-experimental design to test whether exposure to the 1918 influenza pandemic during the fetal stage influenced later life attainment using detailed data on the entire population living in Sweden anytime between 1968 and 2012. In addition, we use rich contextual data on morbidity and mortality, as well as on the socioeconomic status of parents, for the period 1914 to 1922 in order to address issues of selection. We find that the children of mothers exposed during pregnancy to influenza suffered from worse adult health and, for males, also increased mortality at old ages, particularly in cancer. Their income attainment was, however, only weakly – and positively - affected by fetal influenza exposure. We therefore conclude that observed health disadvantage is likely to have been a direct effect of fetal exposure to the 1918 influenza pandemic, remaining latent until later in life.