What Causes Large Spots After Taking Hepatitis A Vaccinnation?

I just went to get a booster for hepatitis A vaccinnation and after about 20 minutes I started noticing very large spots. The first were on the arm and shoulder where the injection was done, but they have spread across my shoulders and the back of my neck. It's about an hour after the vaccine now and I count 10 or so of the spots. They are only a little sore to the touch. Is this anything to worry about?