When children bring viruses home, it can take a heavy toll on younger siblings later in life – University of Copenhagen

Infants exposed to respiratory illnesses via older siblings typically fare worse in terms of education, income and health in adulthood. This is shown by new research from the University of Copenhagen.

You may be familiar with the scenario: your child starts at daycare, 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 hospitalised with respiratory illnesses during infancy compared to 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.

For small 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 N. Meltem 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,’ explains N. Meltem Daysal.

According to the researchers, the likelihood of completing higher education falls by around 0.4 percentage points for children who are exposed to respiratory illnesses as infants. At the same time, as adults, they lose on average just under one per cent in income.

‘A significant proportion of the loss of income can be explained by the fact that illness in infancy affects children’s educational pathways,’ explains N. Meltem Daysal.

The researchers have followed over 1.2 million Danish children from birth into adulthood using detailed register data. They have combined differences in birth order with local variations in disease outbreaks among young children – and in doing so, the researchers have been 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,’ says N. Meltem Daysal.

The results emphasise that preventing illness among infants pays off to a great extent, even in the long term.

‘Through vaccination, good hygiene and support for families with both infants and children in childcare, we can reap benefits that extend far beyond the healthcare system,’ says N. Meltem Daysal.

The study ‘Germs in the Family: The Short- and Long-Term Consequences of Intra-Household Disease Spread’ is published in American Economic Review. Read the full paper here .

Meltem Daysal , Associate Professor Department of Economics, University of Copenhagen Email: meltem.daysal@econ.ku.dk T: +45 35 32 83 47

Simon Knokgaard Halskov UCPH Communications Email: halskov@adm.ku.dk M: +45 93 56 53 29