D1.323 - Assessing Immune Responses to Conjugate Pneumococcal Vaccination in Infants with Transient and Unclassified Hypogammaglobulinemia:Insights from a Tertiary Pediatric Center

Pneumococci (Streptococcus pneumoniae) are among the most important infectious agents of childhood. There are limited number of studies in the literature evaluating pneumococcal antibody levels and vaccine response in patients with a prediagnosis of transient hypogammaglobulinaemia and unclassified hypogammaglobulinemia.

The aim of our study was to serologically and clinically evaluate the pneumococcal antibody levels in patients aged between 24-72 months, whose primary vaccination schedule was completed with PCV13 and who were followed up with a prediagnosis of THI and UH, and to compare them with the pneumococcal antibody levels of healthy children in the same age group whose primary vaccination schedule was completed.

Between January 2024 and July 2024, patients aged between 24-72 months who were admitted to the Pediatric Immunology Allergy Department Outpatient Clinic of our center between January 2024 and July 2024 and who were considered to have transient or unclassifiable hypogammaglobulinaemia according to the diagnostic criteria updated by ESID in 2019 were included in the study after obtaining consent from their parents. All of the patients included in the study were patients who completed the pneumococcal vaccination scheme with PCV13. Healthy children of similar age group, without signs of infection or chronic disease and with complete vaccination according to their age, who applied to the Social Pediatrics Department Polyclinic of our center were included in the study as a healthy control group after obtaining consent from their parents. Venous blood samples of 5 cc each were taken from the children constituting the study and control groups, centrifuged at 4 C⁰ and the 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-PNP 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 response. When the correlation between the time elapsed since the last dose of PCV13 and anti-PNP 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, although not statistically significant. No statistically significant difference was found between the clinical characteristics of the patients and anti-PNP IgG levels (p>0.05).

In conclusion, our study is an important study evaluating pneumococcal antibody levels in patients aged 24-72 months diagnosed with THI and UH. One of the most important results of our study is that, unlike previous studies in the literature, there was no statistically significant difference in anti-PNP IgG levels between patients diagnosed with THI and UH who had completed primary vaccination with PCV13 and the healthy control group.  There is a need for different studies in this patient group in which more patients and healthy children are included, pneumococcal serotype-specific measurements are made and responses to different pneumococcal vaccines are examined.