Longevity of B-Cell and T-Cell Responses After Live Attenuated Influenza Vaccination in Children

Methods.aEuro integral Thirty-eight children (3-17 years old) were administered seasonal LAIV. Blood samples were collected before vaccination with sequential sampling up to 1 year after vaccination. Humoral responses were evaluated by a hemagglutination inhibition assay, and memory B-cell responses were evaluated by an enzyme-linked immunosorbent spot assay (ELISpot). T-cell responses were evaluated by interferon gamma (IFN-gamma) ELISpot analysis, and intracellular cytokine staining of CD4(+) T cells for detection of IFN-gamma, interleukin 2, and tumor necrosis factor alpha was performed using flow cytometry. Results.aEuro integral LAIV induced significant increases in B-cell and T-cell responses, which were sustained at least 1 year after vaccination. Strain variations were observed, in which the B strain elicited stronger responses. IFN-gamma-expressing T cell counts increased significantly, and remained higher than prevaccination levels 1 year later. Expression of T-helper type 1 intracellular cytokines (interleukin 2, IFN-gamma, and tumor necrosis factor alpha) increased after 1 dose and were boosted after the second dose. Hemagglutination inhibition titers were sustained for 1 year. Vaccine-induced memory B cell counts were significantly increased, and the response persisted for one year. Conclusions.aEuro integral LAIV elicited B-cell and T-cell responses that persisted for at least 1 year in children. This is a novel finding that will aid future vaccine policy.