Peer-reviewed article

Are children with inborn errors of metabolism and cystic fibrosis adequately protected? Immunization status and seroepidemiological evaluation of vaccine-preventable diseases.

Gonca Kılıç Yıldırım, Meltem Dinleyici, Ömer Kılıç, Ener Çağrı Dinleyici · 14 May 2026

Abstract

OBJECTIVES: Inborn errors of metabolism (IEMs) are rare genetic disorders associated with increased vulnerability to infections and risk of metabolic decompensation. Although routine immunization is recommended, data on real-world vaccination status, seroprotection rates, and vaccine safety in children with IEMs remain limited. This study aimed to evaluate immunization status, antigen-specific seroprotection rates, determinants of seronegativity, and vaccine safety in a cohort of children with IEMs. METHODS: This single center cross-sectional study was conducted at a tertiary Pediatric Metabolism Unit of Eskişehir Osmangazi University between January and June 2022. A total of 169 children were included. Vaccination history was obtained from immunization cards and parental report. Serological protection was assessed using commercial immunoassays and interpreted according to assay-specific cut-offs. Age eligibility and time since last vaccine dose were analyzed. Descriptive statistics were used to summarize immunization coverage and antibody levels. Group comparisons were performed using chi-square or Fisher's exact tests for categorical variables and non-parametric tests for continuous variables. A p-value <0.05 was considered statistically significant. RESULTS: A total of 169 pediatric patients (52.1 % girls; mean age 65.8 ± 59.6 months) were assessed through medical record reviews and caregiver interviews, with serological testing for vaccine-preventable diseases conducted via standardized ELISA assays. Overall, 94 % of children were vaccinated according to the national immunization program, and no vaccine-related metabolic decompensation or serious adverse events were observed. Six percent were unvaccinated or delayed, mainly due to hospitalization, neurological conditions, pandemic-related disruptions, or parental refusal. Only 9.5 % had received non-scheduled vaccines. Seroprotection was high for tetanus (100 %) and diphtheria (91.7 %). Lower seroprotection was observed for hepatitis B (68.0 %), hepatitis A (53.3 %) and varicella (47.4 %). However, seronegativity was strongly associated with longer time since last dose and age ineligibility for routine vaccination, rather than clear evidence of disease-specific impaired vaccine response. Although numerical differences were observed across metabolic subgroups, no consistent pattern of impaired vaccine response attributable to IEM category was identified. CONCLUSIONS: Children with IEMs demonstrated high overall vaccination coverage and reassuring safety profiles when immunized during metabolically stable periods. Observed immunity gaps were largely explained by programmatic factors, age eligibility, and time since vaccination. These findings support systematic vaccination review and selective serological assessment within routine metabolic follow-up while avoiding overinterpretation of seronegativity as disease-specific immune insufficiency.