Final answer:
The code for the influenza virus is selected based on the structure of its hemagglutinin and neuraminidase proteins. Different subtypes of these proteins are serologically characterized to determine the specific code for each strain. The selected code helps in identifying and tracking different strains of the influenza virus.
Step-by-step explanation:
When the virus that caused the influenza is identified, the code is selected based on the structure of its hemagglutinin and neuraminidase proteins. Influenza viruses have different subtypes of hemagglutinin and neuraminidase, and these subtypes are serologically characterized to determine the specific code. For example, the H1N1 strain is associated with human disease. The selected code helps in identifying and tracking different strains of the influenza virus.