Influenza was first diagnosed in the 1930s and has since been classified into three types: A, B and C. Influenza C has never caused a major epidemic, but A and B each have. Also known as the flu, influenza is a highly contagious virus that can have severe complications. The two strands have different biological mechanisms but are largely similar, especially in the symptoms.
I'm using 487.1 for Influenza unspecified or Flu and 488.02 for type A and B. Please correct me if I'm wrong. Open for suggestions.