Cellular immune responses to influenza. Cellular immune responses, measured as spot-forming units (SFU), indicating the number of interferon (IFN)γ-producing cells per million peripheral blood mononuclear cells (PBMC) from 95 preschool (2–5 years old) children living in Addis Ababa, Ethiopia, after stimulation with (A) whole inactivated influenza A/California/7/2009(H1N1)pdm09 or A/Brisbane/10/2007(H3N2) viruses or with (B) influenza-specific CD4 and (C) CD8 epitopes, derived from internal (i) or external (e) antigens. Zero values were set to 1. Horizontal lines represent mean values. Statistical significance was determined by Mann-Whitney U test; *P < .05.