My son became lactose intolerant after his 5th DTaP. He had a fairly significant reaction and then gut issues for months. He tested negative for food allergies but I finally narrowed down that it was lactose intolerance that lingered. I often wonder if my daughter's dairy and soy sensitivities as an infant were triggered by her 2 month shots, as her symptoms started after that. She outgrew the sensitivities, but she also didn't have any more shots!