Sarcastically, but with some truth, (oxymoron ) I say: If you need flu shots, go to the ER and complain about chest pains.
But I think an ER can't turn you away, and you're brought to front of line if you say you are having chest pains.
I'm not sure how payment/insurance is handled in these cases.
They are billed. If they can't pay then their wages are either garnished or they file chapter 13 or chapter 7 bankruptcy.