Impact of immunization in the neonatal intensive care unit

Introduction. Graduates of the NICU are often underimmunized, perhaps due to provider fear of adverse events following immunizations. Whether changes in clinical status following immunization precipitate the need to rule-out sepsis in infants in the NICU is unknown.Methods. This retrospective cohort study evaluated immunization in infants in the neonatal intensive care unit at the Kaiser Permanente Medical Care Program (KPMCP). Chart reviews were combined with automated databases to obtain information on infants before and after all immunizations and blood cultures.Characteristics of infants by vaccine status at discharge were compared. Kaplan-Meier curves were used to assess timing of immunization among vaccinated infants. Rates of adverse event per day were calculated on the day prior to immunization through four days after, and t-tests used to compare the rates. Self-controlled case series analysis and Poisson regression were used to evaluate the rate of sepsis evaluations compared to a control window.Results. 50.7% of infants were up-to-date at discharge, and 27.0% received no vaccines prior to discharge. Children who received no vaccines had higher gestational ages, higher rates of surgery, and less heart disease and bronchopulmonary dysplasia than vaccinated children.The risk of apnea, but not bradycardia or desaturations, was increased in the postimmunization period compared to the day prior to immunization. The rate of fever was increased for 24-hours following immunization. The incidence rate of sepsis evaluations following immunization was decreased compared to a control window (IRR 0.60, p=0.09).Conclusion. Significant underimmunization was seen in this cohort. Healthier infants appeared to be more vaccinated than less healthy infants, perhaps due to an increased focus on preventive care in these infants. The previously described increase in apnea following immunizations in this population may be a result of the healthy vaccinee effect. Providers may consider deferral of invasive evaluations of post-immunization fevers as clinically indicated. Adverse events following immunization do not appear to cause an increase in sepsis evaluations.