In children, LAIV elicits multifunctional Th1 cells (IFN-γ+/IL-2+/TNF-α+) that persist more than one year, correlating with reduced symptomatic infection despite low serum Hemagglutination inhibition titers [235,236,237], while adults exhibit diminished T cell responses due to pre-existing immunity limiting LAIV replication [237,238]. Here, TNF is linked to infection.