The M protein of influenza viruses has no immunizing effect.

Influenza A virus M protein was prepared by electrophoresis in SDS polyacrylamide gel from virus particles which had been pretreated with octylglucoside to remove the surface glycoproteins; M antigens from the influenza virus strains A/Victoria/3/75 (H3N2), A/FPV/Rostock (Hav1N1) and A/chick/Germany/49 (Hav2Neq1) did not protect mice against a lethal challenge infection with the virulent Victoria strain.