My younger brother (by 7 years) had a 5 hour screaming fit and siezures after getting a vaccination (don't remember which one, I was only 8 or 9). It's one of the clearest memories from that time period that I have. Me standing on the landing, Ian convulsing below just inside the front door, my dad and mom holding him down and trying to keep him from hurting himself.
I know now that it's something like a 1 in 14000 chance but I'm glad that we waited an extra year to start vaccinations and I'm glad we weren't forced to start on someone elses schedule and I'm glad that year of being nervous about measles or whooping cough is over too.