<<Disclaimer: Verify this information before applying it to your situation.>> generally speaking, I do not beleive that a DTP injection, even if it contained gluten, could be harmful. The serum is injected - usually into the thigh here in Canada - and it is my understanding that the gluten has to enter the digestive track to cause damage. I would check with the doctor to clarify if the injection could result in intestinal damage. It is possible that your son had a reaction from the flu shot, not because of any gluten, but maybe from another allergic reaction. It is not uncommon for people to have reactions to vaccines which are egg based, as the flu shot is atleast here in Canada. This ofcourse, is only my opinion and I would suggest that you clarify these points with a physician. Hope this is helpful, Deanna