My son is 18 months old. When he was a newborn, he had a bad reaction to the hepatitis b vaccine and almost died.. Naturally I was terrified and I decided to not get anymore shots for him for a while. I'm feeling less worried and ready to get his shots that he has missed - which is a lot - and was curious if he needs to catch up on them all; like will he still need to get 4 separate doses of a certain vaccine, or will just one be needed?