Antibody response after pneumococcal vaccination in a large cohort of Italian children and adolescents with Down syndrome

Introduction: Pneumococcal vaccination has significantly decreased the burden of invasive pneumococcal disease in the general population, however studies on effectiveness in Down syndrome (DS) are heterogeneous. In this cross-sectional study we evaluated the prevalence of adequate immune response in children with DS after pneumococcal vaccination and we searched for possible clinical predictors associated with it, in order to provide data to optimize vaccination strategies in this high-risk group. Methods: Data of children with DS referred to the DS outpatient Clinic of Bambino Gesù Children's Hospital, Rome, Italy, between September 2021 and March 2022 were reviewed. Clinical and laboratory predictors of immunological response to PCV vaccine, defined as an anti-pneumococcal IgG titer threshold above 0.35 μg/mL were compared and evaluated with bivariate analyses and logistic regression. Results: In this cohort of 406 patients the mean age was 8.4 years and 56.2 % of individuals were male. Most of them had congenital cardiopathy (57.8 %) and recurrent respiratory infections (57.4 %). An anti-pneumococcal Ig titer ≥0.35 μg/mL was found in 50.5 % of patients. Those with Ig < 0.35 μg/mL were significantly younger (p < 0.001) and less likely to have autoimmune disorders or hypothyroidism. Logistic regression showed that a positive history of previous surgery increased the likelihood of Ig ≥ 0.35 μg/mL (OR 2.25, p = 0.001), as well as hypothyroidism (OR 3.14, p = 0.016) and celiac disease (OR 3.70, p = 0.030). Additionally, older age at last PCV13 dose positively correlated with higher Ig levels (p = 0.018). Conclusion: Our findings confirm a lower prevalence of adequate immune response after anti-pneumococcal vaccination in individuals with DS. Older age at last PCV13 dose was found to be correlated to higher specific IgG titers; we suggest a tailored vaccination schedule or a booster dose in individuals with DS that could improve their immune protection.