2. Virology
Influenza A viruses are further divided into subtypes on the
basis of their hemagglutinin (H1 to H17) and neuraminidase
(N1 to N10) activity.8 A third integral membrane protein, the
M2 protein, is also present in small amount on the viral envelope
3 This novel avian influenza A virus (H7N9) differs
genetically from A (H7) and A (N9) viruses that have been