1 May 2026
When sickness spreads at home
New research forthcoming in the American Economic Review shows that early-life exposure to common childhood infections can have lasting consequences
Young children often bring infections home from daycare, preschool, or school. For most family members, these illnesses are temporary inconveniences. But for infants, exposure to respiratory infections during the first months of life can have more serious and lasting effects.
A new article by N. Meltem Daysal, Hui Ding, Maya Rossin-Slater, and Hannes Schwandt, Germs in the Family: The Short- and Long-Term Consequences of Intra-Household Disease Spread, forthcoming in the American Economic Review, shows that common childhood infections can affect children well beyond the initial illness.
Using nearly four decades of Danish administrative data, the researchers study how respiratory diseases spread within families and how early exposure shapes children’s health, education, and labor market outcomes later in life.
The study documents that younger siblings face substantially higher risks of respiratory illness in infancy. Second-born children, who are more likely to be exposed to infections brought home by older siblings, are two to three times more likely to be hospitalized for respiratory conditions before their first birthday than first-born children. The difference is especially pronounced in the earliest months of life, when infants’ lungs, immune systems, and brains are still developing.
To study whether these early exposures have lasting causal effects, the authors combine differences in exposure by birth order with local variation in the prevalence of respiratory disease among young children. This empirical strategy allows them to isolate the consequences of being exposed to more respiratory infections during infancy.
The results show that early-life respiratory disease exposure has consequences that persist into adulthood. Children exposed to higher levels of respiratory disease in infancy experience worse outcomes later in life, including lower educational attainment, lower earnings, more chronic respiratory disease, and more mental health-related outcomes.
The findings highlight an important but often overlooked channel through which health shocks spread within families. Older children can transmit viruses such as RSV, influenza, and other respiratory infections to younger siblings. While these infections are usually mild for older children, they can be much more harmful for infants.
The study also points to concrete policy implications. Measures that reduce infant exposure to respiratory infections may generate benefits that extend far beyond the immediate prevention of illness. These measures include better information for families with newborns and older children, improved hygiene and infection-prevention guidance, and targeted support during high-risk seasons. New preventive tools, such as maternal RSV vaccination and monoclonal antibody treatments for infants, may also play an important role in protecting children at a particularly vulnerable stage of development.
The broader lesson is that everyday infections can have hidden long-term costs. Preventing disease transmission within families is not only a short-term health concern. It may also improve children’s educational, health, and economic outcomes over the life course.
Article: N. Meltem Daysal, Hui Ding, Maya Rossin-Slater, and Hannes Schwandt, Germs in the Family: The Short- and Long-Term Consequences of Intra-Household Disease Spread, forthcoming in the American Economic Review.
The research has been featured in The Economist in the article "Why eldest siblings are brainier"
You can read the research paper the CEBI working paper here