The threat of avian influenza A (H5N1) infection in humans remains a global health concern. Current influenza vaccines stimulate antibody responses against the surface glycoproteins but are ineffective against strains that have undergone significant antigenic variation. An alternative approach is to stimulate pre-existing memory T cells established by seasonal human influenza A infection that could cross-react with H5N1 by targeting highly conserved internal proteins. To determine how common cross-reactive T cells are, we performed a comprehensive ex vivo analysis of cross-reactive CD4 + and CD8 +

A concern was raised that the Vietnamese healthy volunteers examined in the study did not provide written consent. Subsequent investigation has revealed that for these healthy volunteers, only oral and not written consent was obtained; however, this practice was consistent with regulations at the time. The authors mistakenly cited approval by the Oxford Tropical Research Ethics Committee (OxTREC) for this study. Current regulations by Oxford University now stipulate that all human studies obtain institutional approval, and the regulations now require written consent

This is the first report of ex vivo H5 HA-specific T-cell responses in a healthy but H5N1-exposed population. Our results indicate that the presence of H5N1-specific T cells could be an additional diagnostic tool for asymptomatic H5N1 infection.