I had a dpt shot in 1986 and was sick for the following four days; what is the probability that i will react again?

Different vaccine: Before about 1992 the DPT had a whole cell pertussis component that often caused fever & swelling. It was rarely given after 5 due to its high reaction rate. After '92, a restructured vaccine has a lab designed pertussis component that changed things for the better.Now the dtap is one of the least likely to have a reaction & various forms are given to folks at all ages. I doubt you'll have a rxn.