Good question. Probably worth asking the CDC about. I'm sure it's partly a cost/benefit decision. There is probably limited capacity for vaccine testing, production (and delivery) and producing vaccines against strains that are not expected to be active that season might be pointless and take away from production and distribution of others. From a practical point of view, if it's difficult to get everyone to take one shot, I imagine that trying to educate the public about 2 vaccine versions would be a public health headache. Many of the people I know, who I would have expected to be more informed, still complain when they get colds despite having had a flu vaccine shot. The cold vs flu difference must have been explained in a million different places by now.
I did look at some pages of the CDC site and vaccine shots traditionally protected against 3 strains but that 4-strain versions are also now popular. I'm left with the impression that combining them into into one shot is not a trivial matter.
On a personal note, and as an aside, I also know some people who resent being encouraged by their government to take vaccines, some kind of "rebellion" against the "man". It's difficult for me to take this seriously considering the large number of people who buy illegal drugs manufactured by criminals.
But Robert, those friendly, encouraging suppliers are "my" Man, who is somebody other than "the" Man.
The magic lives in the pronoun. Or so I believe.
