Cellular Immune Responses in Children and Adults Receiving Inactivated or Live Attenuated Influenza Vaccines

TLDR

The patterns of cellular immune responses induced by live attenuated versus trivalent inactivated influenza vaccines have not been extensively studied, particularly in children. The study aimed to compare the effects of TIV and LAIV on cellular immunity to live influenza A virus in children and adults and to identify factors influencing response variability. IFN‑γ flow cytometry was used to quantify IFN‑γ+ NK and T cells in peripheral blood mononuclear cells stimulated with live influenza A virus before and after vaccination. LAIV significantly increased influenza‑A–specific IFN‑γ+ CD4 and CD8 T cells in 5‑to‑9‑year‑old children, TIV did not; in 6‑month‑to‑4‑year‑old children TIV increased T‑cell responses (LAIV not evaluated); adults showed no vaccine‑induced increases, and post‑vaccination changes were highly variable and inversely related to pre‑vaccination levels, especially of CD56(dim) NK cells, underscoring age, vaccine type, and baseline immunity as key determinants of cellular response magnitude.

Abstract

The patterns of cellular immune responses induced by live attenuated influenza vaccine (LAIV) versus those of the trivalent inactivated influenza vaccine (TIV) have not been studied extensively, especially in children. The goals of this study were to evaluate the effects of TIV and LAIV immunization on cellular immunity to live influenza A virus in children and adults and to explore factors associated with variations in responses to influenza vaccines among individuals. A gamma interferon (IFN-gamma) flow cytometry assay was used to measure IFN-gamma-producing (IFN-gamma+) NK and T cells in peripheral blood mononuclear cell cultures stimulated with a live influenza A virus strain before and after LAIV or TIV immunization of children and adults. The mean percentages of influenza A virus-specific IFN-gamma+ CD4 and CD8 T cells increased significantly after LAIV, but not TIV, immunization in children aged 5 to 9 years. No increases in the mean levels of influenza A virus-reactive IFN-gamma+ T cells and NK cells were observed in adults given LAIV or TIV. TIV induced a significant increase in influenza A virus-reactive T cells in 6-month- to 4-year-old children; LAIV was not evaluated in this age group. The postvaccination changes (n-fold) in the percentages of influenza A virus-reactive IFN-gamma+ T and NK cells in adults were highly variable and correlated inversely with the prevaccination percentages, in particular with that of the CD56(dim) NK cell subset. In conclusion, our findings identify age, type of vaccine, and prevaccination levels of immune reactivity to influenza A virus as factors significantly associated with the magnitude of cellular immune responses to influenza vaccines.