Immune response after influenza vaccination in children with cancer

Purpose. To assess the immune response to inactivated trivalent split influenza vaccine in children with cancer. Procedures. Forty-four children with various types of malignancies received two doses of influenza vaccine 2-4 weeks apart. Hemagglutinin-inhibition (HI) antibody titers were determined in paired sera obtained just before the first vaccination and 4 weeks after the second vaccination. Results. Influenza vaccine was administered to all children without any serious adverse effects. Protective titer rates (proportion of patients achieving antibody titers ≥40 among those with pre-vaccination titers <40) and response rates (proportion of patients with fourfold or more antibody rise) were 72% and 65% for H1N1, 60% and 40% for H3N2, and 38% and 46% for influenza B, respectively. However, patients on chemotherapy showed a significantly lower immune response to influenza A than those having completed chemotherapy; protection titer rates were 42% versus 90% for H1N1 (P = 0.006) and 25% versus 83% for H3N2 (P = 0.019). For influenza B, patients with low IgG showed a lower response rate than those with high IgG (29% vs. 61%, P = 0.040). Multivariate analysis revealed that factors significantly associated with a lower immune response were low IgG (P < 0.001) and administration of chemotherapy (P = 0.003) for H1N1, administration of chemotherapy (P = 0.008) for H3N2, and low white blood cell (WBC) count (P = 0.030) and low IgG (P = 0.030) for influenza B. Conclusions. Influenza vaccination given to children with cancer was safe and induced immune reaction comparable to healthy children, although patients on chemotherapy and/or with chemotherapy-related conditions had a limited ability to produce a sufficient immune response.