The trend in the formation of postvaccinal antibodies (Ab) to a mixture of S. pneumoniae polysaccharides (PS) was studied in 100 Pneumo 23-vaccinated children and adolescents with type 1 diabetic (T1D) (Group 1, n = 72) and its combination with the subunit vaccine Grippol (Group 2, n = 28). Following 1-1.5 months, the protective level of Ab l 40 conventional units (CU/ml) was revealed in 95.1 and 85.2% of Groups 1 and 2, respectively; and after 1 year, this was in 55.1 and 37%, respectively (p > 0.05). The level of formation of IgG Ab to a PS mixture did not depend on the age of patients, the duration of T1D, the presence of late diabetic complications. A relationship was found between the formation of postvaccinal Ab and their baseline level: in patients with very low (< 10 CU/ml) and low (10-20 CU/ml) levels of Ab after administration of pneumococcal vaccine, the level of IgG Ab to a S. pneumoniae PS mixture increased by 8.8-4.1 times in the early periods and exceeded the baseline levels by 4.8-2.8 times, respectively. The putative protective level of IgG AB to a S. pneumoniae PS mixture is proposed to be l 20 CU/ml.