No one I know has ever gotten sick from a flu shot. The worse was my mom was a little achy after the first few times, the doctor told her itwas just her body reacting to the protiens in the shot. It won't make you sick (stomach or otherwise) as for mercury I'm pretty sure they don't put it in there, if it makes you feel better ask the doctor or nurse who administers it then you don't even have to wonder. I really don't think they'd do that since they give it to pregnant women and children and preg women aren't allowed too much of certain fish because of mercury levels. Good luck!
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Johann Wolfgang von Goethe
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Benjamin Franklin