Impaired immune response to polysaccharide antigens and warning signs in children with recurrent respiratory infections.

Introduction. Inborn errors of immunity constitute a group of genetic disorders that may present with warning signs. Among their most common presentations are recurrent respiratory infections, which may reflect abnormalities in humoral immunity. In this context, specific antibody deficiency (SAD) is characterized by an inadequate response to polysaccharide antigens, with normal serum immunoglobulin levels and antibody responses to protein antigens. Objective. To identify SAD by testing for antibodies against Streptococcus pneumoniae in pediatric patients with recurrent respiratory infections and to describe the presence of the Jeffrey Modell Foundation warning signs.Population and methods. Observational, analytical, and retrospective study. Pediatric patients with recurrent respiratory infections were included. Baseline levels of anti-S. pneumoniae were measured; when values were ≤113 mg/L, the 23-valent pneumococcal polysaccharide vaccine was administered, and the post-vaccination response was evaluated. SAD was defined as the absence of an adequate serological response (post-vaccination titer ≤113 mg/L). Warning signs were analyzed descriptively in patients with SAD.Results. A total of 146 patients were included; 50.68% had anti-pneumococcal IgG levels ≤113 mg/L; of these, 18% remained low after vaccination, and SAD was diagnosed (prevalence: 8.9%). Among patients with SAD, a proportion exhibited three or more warning signs. Conclusion. SAD was a common finding in children with recurrent respiratory infections. The presence of warning signs could help identify patients who require immunological evaluation.