Overview
- A University of Copenhagen working paper using decades of Danish records finds second-borns earn 1.9% less than their firstborn siblings by age 30.
- The study reports younger siblings are two to three times more likely to be hospitalized for respiratory illness in their first year, with the gap sharpest in the first three months.
- Researchers argue firstborn toddlers often pick up viruses in daycare and carry them home to infant siblings who are at a vulnerable stage of lung and brain development.
- The authors estimate early-life infections could explain about half of the earnings gap and note other factors like diluted parental attention and the sibling “teaching effect” likely matter.
- Coverage highlights simple steps such as keeping vaccinations current and keeping sick children home, with a reminder that the findings are from a working paper and have not yet been peer reviewed.