M2e, human, consisting of the 23 extracellular residues of M2 (the third integral membrane protein of influenza A), has been remarkably conserved in all human influenza A, which is a valid and versatile vaccine candidate to protect against any strain of human influenza A[1].
[1]. De Filette M, et al. Improved design and intranasal delivery of an M2e-based human influenza A vaccine. Vaccine. 2006 Nov 10;24(44-46):6597-601.