The H1N1 and H3N2 viruses both cause the flu, an infectious disease characterized by respiratory symptoms, fever, and body aches. Each year, a flu vaccine that contains H1N1 and H3N2 antigens is developed. An individual who receives the vaccine makes antibodies directed against these antigens.

The flu vaccine is typically about 60% effective against H1N1 flu viruses, but only 30% effective against H3N2 viruses. What is the most likely reason why the flu vaccine is less effective against the H3N2 flu viruses than the H1N1 flu viruses?

A. Infection with the H1N1 virus does not involve an immune system response.
B. Infection with the H3N2 virus does not involve an immune system response.
C. The H3N2 flu viruses mutate more rapidly than the H1N1 flu viruses.
D. The H1N1 flu viruses mutate more rapidly than the H3N2 flu viruses.