The influenza A(H1N2) strain appears to have resulted from the reassortment of the genes of the currently circulating influenza A(H1N1) and A(H3N2) subtypes. Influenza viruses can be divided into two types, influenza type A viruses and influenza type B viruses. Influenza A viruses can be further divided into subtypes on the basis of two proteins, hemagglutinin (H) and neuraminidase (N), found on the surface of the virus. Since 1977, two influenza A subtypes, A(H1N1) and A(H3N2), have circulated widely among people. The hemagglutinin protein of the A(H1N2) virus is similar to that of the currently circulating A(H1N1) viruses and the neuraminidase protein is similar to that of the current A(H3N2) viruses.