Influenza viruses are categorized as three types: A, B and C. The seasonal flu that we get every year is caused by the human influenza A and B viruses.
Influenza C virus causes only mild respiratory illnesses and are not dangerous enough to cause an epidemic.
According to the CDC, Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: the hemagglutinin (H) and the neuraminidase (N). There ...