Firstborn Children More Likely to Be Up to Date on Vaccinations Than Non-firstborn Children

Firstborn U.S. children were more likely to be fully up to date on their childhood vaccines than non-firstborn children, according to an analysis of a national dataset to be published in the October 2022 Pediatrics. The research brief, “Birth Order and Up-To-Date Vaccination Status,” also published online Wed. Sept. 7, compared vaccination up-to-date status between firstborn and non-firstborn children using the 2016-2019 National Immunization Survey-Child dataset. Researchers reviewed data on 24,582 firstborn and 37,761 non-firstborn children to check if they received vaccines that are recommended before age 19 months. After adjusting for sociodemographic variables, firstborn children were significantly more likely to be up to date for all eight individual vaccines and all four vaccine series examined. When the number of children under age 18 in the household was introduced as a control, the results were attenuated, suggesting that family size may partially, but not fully, explain these results, according to the study. The authors suggest that future research is conducted to explain this trend.

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The American Academy of Pediatrics is an organization of 67,000 primary care pediatricians, pediatric medical subspecialists and pediatric surgical specialists dedicated to the health, safety and well-being of infants, children, adolescents and young adults.