ORIGINAL ARTICLE Underimmunization at discharge from the neonatal intensive care unit AM Navar-Boggan 1,2 , NA Halsey 2 , GJ Escobar 3 , WC Golden 4 and NP Klein 5 1 Departments of Internal medicine and Pediatrics, Duke University Medical Center, Durham, NC, USA; 2 Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA; 3 Division of Research, Kaiser Permanente Northern California and Division of Research, Perinatal Research Unit, Oakland, CA, USA; 4 Eudowood Neonatal Pulmonary Division, Johns Hopkins University School of Medicine, Baltimore, MD, USA and 5 Kaiser Permanente Vaccine Study Center, Oakland, CA, USA Objective: The objectives of this study are to determine immunization rates at discharge from the neonatal intensive care unit (NICU) among infants 2 months of age and above and to evaluate risk factors for underimmunization. Study Design: A retrospective cohort study was performed for infants in six NICUs in the Northern California Kaiser Permanente Medical Care Program. Immunization status at discharge was determined for all infants discharged on or after age 60 days. Logistic regression was used to identify risk factors for underimmunization at the time of discharge. Result: Of 668 infants discharged on or after age 60 days from the NICU, 51% were up-to-date for routine immunizations. Twenty-seven percent of infants had received no vaccines. Factors associated with higher immunization rates at discharge include history of mechanical ventilation, congenital heart disease and a diagnosis of apnea or bronchopulmonary dysplasia during the NICU stay, whereas surgery was associated with lower immunization rates. Conclusion: A significant proportion of infants discharged on or after 2 months of age in the NICU in this health system was unimmunized or underimmunized at discharge. Further efforts should be made to improve immunization rates prior to discharge. Journal of Perinatology (2012) 32, 363–367; doi:10.1038/jp.2011.111; published online 11 August 2011 Keywords: neonatal intensive care unit; immunization; underimmunization; delayed immunization Introduction Infants in the neonatal intensive care unit (NICU) are at risk for future underimmunization. Low birth weight (less than 2500 g) children have been shown to have increased rates of underimmunization at both 24 1 and 36 months 2 of age. Other studies have found that lower gestational age is also associated with decreased immunization rates. 3 Infants in the NICU are at particularly high risk of delayed immunization. A study of infants discharged from the special care nursery found that >50% of all infants were not up-to-date on immunizations at 6 months of age. In very low birth weight infants in the same cohort, underimmunization (not up-to-date) rates were >90%. 4 Davis et al. 5 demonstrated that infants who spent time in the NICU were less likely to be fully vaccinated at 12 and 24 months of age than their age-matched peers. Studies of immunization rates in infants discharged from the NICU (preterm and low birth weight infants) are often conducted in children of 1 year or older. By this age, most children who spent time in the NICU have been discharged and are cared for by primary health care providers. A subset of preterm and low birth weight infants, however, remains in the NICU beyond 2 months of age, when they become eligible to receive routine childhood immunizations other than hepatitis B vaccine. Immunization rates in this subset of infants have not been studied. High rates of immunization are theoretically attainable in the NICU, where all infants have access to healthcare, but may be limited by lack of provider knowledge about vaccine recommendations or concerns about potential adverse events. Because immunization delay in infancy contributes to underimmunization at later ages, it is important to identify when the delay begins. 1,2,4,5 We evaluated immunization rates in a cohort of infants who remained in the NICU beyond 2 months to determine immunization rates in infants 60 days of age or older, as they are discharged from the NICU. Methods We recently reported the results of a retrospective cohort study of infants in all six level-three NICUs in the Northern California Kaiser Permanente Medical Care Program (KPMCP). 6 The goal of that previous study was to evaluate apnea, following routine Received 26 April 2011; revised 8 July 2011; accepted 19 July 2011; published online 11 August 2011 Correspondence: Dr AM Navar-Boggan, Duke University Medical Center and Johns Hopkins Bloomberg School of Public Health, 615 N Wolfe Street, Room W5041, Baltimore, MD 21205, USA. E-mail: ann.navar@duke.edu Journal of Perinatology (2012) 32, 363–367 r 2012 Nature America, Inc. All rights reserved. 0743-8346/12 www.nature.com/jp