Vaccines Are Not Associated With Metabolic Events in Children With Urea Cycle Disorders

Abstract

BACKGROUND: Despite the success of childhood immunizations in prevention of infectious diseases, questions remain about the safety of vaccines in medically fragile children with inborn errors of metabolism such as urea cycle disorders (UCDs). Patients with UCDs are subject to hyperammonemic episodes (HAEs) after infection, fever, or other stressors. OBJECTIVE: We sought to assess the risk of HAEs that required urgent care or hospitalization after routine vaccinations in pediatric patients with underlying UCDs. METHODS: This was a retrospective investigation of vaccine safety in children with UCDs within the longitudinal Rare Diseases Clinical Research Consortium for UCD. Postvaccination exposure periods were defined as 7 or 21 days after any immunization. The association of vaccines and HAEs was modeled by using conditional Poisson regression, adjusting for age, and using a self-controlled case series method including all patients with ≥1 HAE and with any vaccine exposure. RESULTS: The study enrolled 169 children younger than 18 years. Of these children, 74 had records of at least 1 HAE and at least 1 vaccination. With adjustment for age, there was no increase in relative incidence of HAEs in either the 7-day (1.31 [95% confidence interval (CI): 0.80–2.13]) or 21-day (1.05 [95% CI: 0.74–1.47]) exposure period after vaccination compared with HAEs outside of the vaccination periods. No vaccine type was associated with significantly more HAEs. CONCLUSIONS: We found no statistically significant association between childhood immunizations and HAEs in children with UCDs. The results support the safety of immunization in this medically vulnerable population.