If they're free and relatively easy to get, I think that should be the standard.
Great so everyone has to go get a Flu Shot before voting.
Free and easy to get.
If you don't get a flu shot, you can't vote.
What, you didn't have time? No voting for you.
You didn't want one? No voting for you.
You don't live near someplace that offers a free and easy flu shot? No voting for you.
You didn't know that you had to get one to vote? No voting for you.
You meant to but forgot? No voting for you.
You don't have a car, and public transportation is terrible, and so you had no way to get one? No voting for you.
You got a flu shot but left proof at home? No voting for you.
Excellent logical fallacy, sir!