first flu vaccine

My son just received his flu shot and now he is running a fever, has chills and he also threw up twice. We took him to urgent care immediately and they told us to give him infant Advil. 
I have been reading about the flu vaccine and I have read so many awful things. Now, I am laying here at night wondering if my son will be okay and if he will develop fine. I had no idea that the flu vaccine contains mercury, I thought that mercury was removed from all vaccines.
To the other moms out there, were your children fine after the vaccine? Did they get sick? Did they developed well?