Yearly Vaccination of Humans for Influenza Viruses Is Necessary Because

Multiple Choice

Yearly vaccination of humans for influenza viruses is necessary because ________.

A) of an increase in immunodeficiency diseases
B) the flu can generate anaphylactic shock
C) surviving the flu one year exhausts the immune system to nonresponsiveness the second year
D) rapid mutation in flu viruses alters the surface proteins in infected host cells