HealthDay News — First-born children are more likely to be up-to-date (UTD) on vaccinations, according to a research brief published online September 7 in Pediatrics.

Allison Lin, from the Steven and Alexandra Cohen Children’s Medical Center of New York in Lake Success, and colleagues conducted a cross-sectional study using the 2016 to 2019 National Immunization Survey-Child data (62,343 participants). The likelihood of vaccination UTD status was examined as a function of the child’s first-born status. The eligible sample included 24,582 first-born children and 37,761 non-first-born children (38.68 and 61.32 percent, respectively).

After adjusting for sociodemographic variables, the researchers found that first-born children were significantly more likely to be UTD for all 8 individual vaccines and all 4 vaccine series examined. When the number of children younger than 18 years in the household was included as a control into the multivariate models, first-born children were significantly more likely to be UTD for 4 of 8 individual vaccines, specifically pneumococcal conjugate vaccine and diphtheria, tetanus, and acellular pertussis (adjusted odds ratios, 1.30 and 1.29, respectively, compared with non-first-born children). The likelihood of being UTD for all vaccination series was also significantly increased for first-born children.

“Because delays in vaccination may be exacerbated by the coronavirus disease 2019 pandemic, prompt intervention to address worsening disparities in vaccination coverage is of vital importance,” the authors write.

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