Pneumococcal Serological Evaluation in Vaccinated Children Diagnosed With Transient Hypogammaglobulinemia of Infancy and Unclassified Hypogammaglobulinemia

The severity and incidence of invasive pneumococcal infections increase in inborn errors of immunities. However, there are limited number of studies in the literature evaluating pneumococcal antibody levels in patients with a prediagnosis of transient hypogammaglobulinaemia (THI) and unclassified hypogammaglobulinemia (UH). The aim of our study was to serologically evaluate pneumococcal antibody levels in children aged 24–72 months with THI or UH who had completed the primary PCV schedule, and to compare these levels with those of age matched healthy control. Patients aged between 24-72 months who were admitted to the Pediatric Immunology Allergy Department Outpatient Clinic between January 2024 and July 2024 and who were considered to have transient or unclassifiable hypogammaglobulinaemia. Healthy children of similar age group, without signs of infection or chronic disease and with complete vaccination according to their age were included in the study as a healthy control group. Serum samples obtained were separated and stored at -20 C⁰ until the day anti-PNP IgG levels were studied by ELISA method. No statistically significant difference was found when anti-PCP IgG levels were compared according to the diagnosis of THI and UH in the patient group (p=0.410). It was determined that both patient groups produced similar antibody levels. There were no statistically significant differences in anti PCP IgG levels between patients and control group (p=0.427). When the correlation between the time elapsed since the last dose of PCV13 and anti-PCP IgG levels was evaluated in the patient group (both in all patients and age groups) and in the control group, no statistically significant correlation was found. In the patient group, anti-PNP IgG levels were found to be lower in the group in which both IgG and IgM values were low compared to the other groups. No statistically significant difference was found between the clinical characteristics of the patients and anti-PCP IgG levels. In conclusion, this study is one of the few to evaluate pneumococcal antibody levels in children with THI and UH who have completed the primary PCV13 vaccination series. Further prospective studies involving serotype-specific tests and different pneumococcal vaccine formulations are needed.