Assessment of Infant Growth and Health Care Utilization Following Tetanus, Diphtheria, Pertussis (tdap) Vaccination During Pregnancy and Lactation

BACKGROUND:There are limited data on infant growth and healthcare utilization following perinatal Tdap vaccination. OBJECTIVE:To assess associations of Tdap vaccination during pregnancy or when given to lactating individuals with infant growth and healthcare utilization. STUDY DESIGN:We conducted a retrospective cohort study using electronic health records from two US healthcare systems. Prenatal care patients with a singleton live birth (2014-2022) and their linked infants were included. For pregnancy analyses, we compared outcomes in infants of those who received Tdap vaccination at ≥27 gestational weeks to those with no Tdap up to 90 days after delivery. For postpartum analyses, restricted to human milk feeders, we compared Tdap vaccination within 90 days after delivery versus none. Infant growth outcomes assessed between 3 and 12 months of age were growth faltering and slow weight gain (<5th percentile). Infant healthcare utilization outcomes were counts of outpatient visits, including well visits, and emergency department (ED) visits up to 6 months after delivery, excluding uninsured infants. We estimated adjusted prevalence ratios (aPR), or rate ratios (aRR), and 95% confidence intervals (CI). RESULTS:There were 33,261 and 25,335 pregnancies eligible for infant growth and healthcare utilization analyses, respectively. Tdap vaccination during pregnancy was not associated with growth faltering (aPR: 0.96, 95% CI: 0.85-1.09), slow weight gain (aPR: 0.93, 95% CI: 0.81-1.07) or ED visits (aRR: 1.00, 95% CI: 0.84-1.18), but was slightly associated with the rate of outpatient visits (aRR: 1.07, 95% CI: 1.01-1.12). No associations were observed among the 3034 and 3191 lactating individuals eligible for infant growth and healthcare utilization analyses, respectively. CONCLUSION:Tdap vaccination during pregnancy was not associated with adverse infant growth outcomes or ED visits. Although Tdap vaccination during pregnancy was associated with a slight increase in outpatient visits per infant, residual confounding by health seeking behavior could not be ruled out.