Subcategories

• Influenza A

  Influenza A virus, typically encountered more frequently than types B and C, and associated with the majority of serious epidemics, can be further subdivided into strains or subtypes based on antigenic differences in the external hemagglutinin proteins (H1-H16) and neuraminidase proteins (N1-N9).

• Influenza B

  Influenza B virus is predominantly a human pathogen, although it has been found to infect seals. The limited host range of influenza B and a slower rate of mutation than influenza A appears to preclude development of influenza B pandemics, but influenza B is a significant human pathogen and on an individual basis, infection may result in death.