BACKGROUNDThe American Academy of Pediatrics recommends birth doses of vitamin K, erythromycin ointment, and the hepatitis B vaccine, but the relationship between birth medication administration and childhood immunization compliance is understudied. The objective of this study is to evaluate rates of newborn medication administration, and risk factors for refusal in military beneficiaries and determine the relationship between medication refusal and under-immunization at 15 months.METHODSA retrospective chart review was completed for all term and late preterm infants born at Brooke Army Medical Center, San Antonio, TX, from January 1, 2016, to December 31, 2019. The electronic medical record was queried for birth medication administration, maternal age, active-duty status, rank, and birth order. Childhood immunization records were extracted for all patients who continued care at our facility. A patient was considered completely immunized if they had received at least 22 vaccines by 15 months: three doses of the hepatitis B vaccine [PediarixTM], two doses of the rotavirus vaccine [RotarixTM], four doses of the DTAP vaccine [PediarixTM and Acel-ImmuneTM], three doses of Haemophilus influenza B vaccine [PedvaxhibTM], four doses of pneumococcal [Prevnar 13TM], three doses of IPV [PediarixTM], one dose of measles, mumps, and rubella [MMRTM], one dose of varicella [VarivaxTM] and one dose of hepatitis A vaccine [HarvixTM].RESULTSSeven thousand one hundred and forty infants were included; 99.3% received vitamin K, 98.8% received erythromycin ointment, and 93.8% received the hepatitis B vaccine. Refusal of the erythromycin ointment and hepatitis B vaccine was associated with older maternal age and higher birth order. Childhood immunization records were available for 607 infants; 7.2% (n = 44) were under-immunized by 15 months, with no infants being non-immunized. Refusal of the hepatitis B vaccine (RR: 2.9 (CI 1.16-7.31)) only at birth was associated with a higher risk of being under-immunized.CONCLUSIONSRefusal of the hepatitis B vaccine in the nursery is associated with a risk of being under-immunized in childhood. Obstetric and pediatric providers should be aware of this association for appropriate family counseling.