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Schematic figure of influenza virus. On the surface of the virus there are three viral proteins, haemagglutinin (HA), neuraminidase (NA) and the matrix 2 protein (M2). Underlining the viral envelope is the matrix 1 protein (M1), the nucleoprotein (NP) encapsidates the genome segments with one complex of the polymerase attached (PB1, PB2 and PA). The non-structural protein 2 (NS2) is also contained in the virion in low numbers.
