Identification of an epitope of limited variability under strong immune selection in the haemagglutinin head domain of H1N1 influenza

Antigenic targets of influenza vaccination are currently seen to be polarised between (i) highly immunogenic (and protective) epitopes of high variability, and (ii) conserved epitopes of low immunogenicity. This requires vaccines directed against the variable sites to be continuously updated, with the only other alternative being seen as the artificial boosting of immunity to invariant epitopes of low natural efficacy. However, theoretical models suggest that the antigenic evolution of influenza is best explained by postulating the existence of highly immunogenic epitopes of limited variability. A corollary of this model is that a 9universal9 influenza vaccine may be constructed by identifying such protective epitopes of low variability and these vaccines would also have the potential to protect against newly emerging influenza strains. Here we report the identification of such an epitope of limited variability in the H1 head domain of the haemagglutinin protein that could be exploited to produce a universal vaccine for the H1 subtype of influenza A.