A 5-year-old child is ill with measles. Blood analysis revealed increase of total number of leukocytes up to 13 × 109/l. Leukogram: basophils - 0, eosinophils - 1, myelocytes - 0, juvenile neutrophils - 0, band neutrophils - 2, segmented neutrophils - 41, lymphocytes - 28, monocytes - 28. Name this phenomenon: