The CDC recommends a yearly flu vaccine as the most important step in protecting against influenza and its potentially serious complications. The seasonal flu vaccine protects against the three or four influenza viruses that research indicates will be most common during the upcoming season. If you do get a flu shot, you can still possibly get the flu. Using the illustration and prompt, explain how this can happen. All BUT ONE choice could apply.
A Variation in the influenza virus population always exists.
B The influenza virus mutates rapidly, from season to season.
C Once subjected to the vaccine, the virus begins to evolve and become resistant.
D You are exposed to an influenza virus that was not included in the seasonal vaccine.