Nine neuraminidase subtypes are known; many occur only in various species of duck and chicken. Subtypes N1 and N2 have been positively linked to epidemics in man, and strains with N3 or N7 subtypes have been identified in a number of isolated deaths.

The neuraminidase enzyme exists as a mushroom-shape projection on the surface of the influenza virus. It has a head consisting of four co-planar and roughly spherical subunits, and a hydrophobic region that is embedded within the interior of the virus' membrane. It is comprised of a single polypeptide chain that is oriented in the opposite direction to the hemagglutinin antigen. The composition of the polypeptide is a single chain of six conserved polar amino acids, followed by hydrophilic, variable amino acids.

Neuraminidase has functions that aid in the efficiency of virus release from cells. Neuraminidase cleaves terminal sialic acid residues from carbohydrate moieties on the surfaces of infected cells. This promotes the release of progeny viruses from infected cells. Neuraminidase also cleaves sialic acid residues from viral proteins, preventing aggregation of viruses. Administration of chemical inhibitors of neuraminidase is a treatment that limits the severity and spread of viral infections. Neuraminidase is also a virulence factor for the bacteria Bacteroides fragilis.

Inhibitors are used for combating the virus. They are zanamivir and oseltamivir .

Hemagglutinin, Antigenic shift, EC 3.2.1, Viral enzymes, Influenza, Avian Influenza H5N1.