In almost all cases, an adverse reaction is caused by something that would have made the vaccine containdicated in the first place. It doesn't negate the adverse affects to 0, but in general, vaccines are incredibly safe, and having a severe outlier reaction is likely a smaller probability than getting struck by lighting.
How about this, studies have repeatedly shown that Vaccines are safe, including the largest study ever completed, that showed there was no correlation between getting vaccines and autism. There are only 2-3 studies that I am aware of that created some concerns over the safety of vaccines, but both had major issues, and it appears that the correlation was related to factors other than vaccines. Bonzo, please continue to argue in circles.