A B C
Influenza viruses come in three types: A, B and C. How any one virus acquires its identification letter depends on differences in the matrix protein, nucleoprotein and response of antibodies to a particular strain. Influenza A is the most dangerous for humans, influenza C is the least dangerous.
H & N
The H stands for one of the 16 different hemagglutinin
proteins contained in a virus that allows it to penetrate a foreign body. The "N" stands for another protein in the genetic make-up of a flu virus called neuraminidase
, of which there currently exist nine variations.