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Infants exposed to respiratory illnesses through older siblings typically fare worse in education, income and health in adulthood, according to new research from the University of Copenhagen.
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The research is published in the journal American Economic Review.
You may be familiar with the scenario: Your child starts day care, and soon the whole household is struck down with a virus. It's a nuisance for everyone, but infants are particularly vulnerable when older siblings bring viruses home.
'We see that second-born children have a two- to three-times higher risk of being hospitalized with respiratory illnesses during infancy compared with first-born children at the same age. This is particularly pronounced in the first six months of life, when children are biologically most vulnerable,' says N. Meltem Daysal, associate professor at the Department of Economics and CEBI.
Early infection impairs education and income
For young children infected by older siblings, however, the consequences can extend far beyond the acute illness. In fact, respiratory illness in the first months of life can leave its mark on education, income and health many years later, according to a new study led by Daysal and her research colleagues.
'When we compare siblings, we can see that early exposure to illness is linked to a lower likelihood of completing both secondary school and higher education—and to lower income later in life,' Daysal explains.
According to the researchers, the likelihood of completing higher education falls by around 0.4 percentage points for children exposed to respiratory illnesses as infants. At the same time, as adults, they have, on average, just under 1% lower income.
'A significant proportion of the loss of income can be explained by the fact that illness in infancy affects children's educational pathways,' Daysal explains.
Prevention pays off
The researchers followed more than 1.2 million Danish children from birth into adulthood using detailed register data. They combined differences in birth order with local variations in disease outbreaks among young children and, in doing so, were able to isolate the effect of exposure to illness in infancy from other family and background factors.
'By combining variation in birth order with local disease outbreaks, we are able to identify causal effects—not just correlations,' Daysal says.
The results emphasize that preventing illness among infants pays off substantially, even in the long term.
'Through vaccination, good hygiene and support for families with both infants and children in child care, we can reap benefits that extend far beyond the health care system,' Daysal says.
More information: N. Meltem Daysal et al, Germs in the Family: The Short- and Long-Term Consequences of Intrahousehold Disease Spread, American Economic Review (2026). DOI: 10.1257/aer.20231521
Provided by University of Copenhagen
This story was originally published on Phys.org.
