Efficacy of OM-85 in Children with Recurrent Respiratory Tract Infections: Relationship with Allergic and Immunological Features

OM-85 is an immunomodulatory agent used for the prevention of recurrent respiratory tract infections (RTIs) in children; however, the influence of allergic and immunological characteristics on treatment response remains unclear. This study evaluated changes in infection frequency before and after OM-85 treatment and examined whether treatment response was associated with allergic status or immunological characteristics. This single-center, retrospective cohort study included 114 children treated with OM-85 for recurrent RTIs. Annual upper (URTI) and lower (LRTI) respiratory tract infection episodes before and after treatment were compared. Treatment responses were analyzed according to atopic status, inhalant allergen sensitization, and immunoglobulin status (normal, transient hypogammaglobulinemia, and partial IgA deficiency). Independent predictors of post-treatment infection burden were assessed using multivariable linear (ANCOVA) and negative binomial regression analyses. The median age was 56.5 months; 46.5% of patients were atopic, 28.1% had partial IgA deficiency, and 8.8% had transient hypogammaglobulinemia. Following OM-85 treatment, median annual URTI episodes decreased from 8 to 5 (40.6%; p<0.001; r=0.78), and LRTI episodes from 1 to 0 (63.2%; p<0.001; r=0.54). The proportion of children with frequent URTIs (≥6/year) declined from 84.2% to 33.3%, and those with at least one LRTI episode from 60.5% to 32.5%. The reduction was significant in both atopic and non-atopic patients and in subgroups with normal or low immunoglobulin levels. In multivariable analysis, the only independent predictor of post-treatment burden was baseline infection burden. OM-85 treatment was associated with a reduction in both upper and lower respiratory tract infection frequency independently of allergic status and serum immunoglobulin level, with baseline infection burden being the factor most strongly associated with post-treatment infection burden. The greatest clinical benefit is expected in children with frequent infections, and this group may constitute a priority target population for this preventive strategy.