Why does the H1N1 Vaccine hurt so much?

The H1N1 shot is intermuscular, meaning it is administered into your muscles (not your veins). The amount of vaccine is also a little bit bigger than the seasonal flu shot. Therefore, some people experience pain in their arm. It has nothing to do with a punctured vein because the needle goes into your muscles. Different muscles surround the sight of injection. Your deltoid is one of these muscles and is around your shoulder (perhaps this is why your shoulder hurts...after all, it did get pricked with a needle...) It really doesn't have anything to do with the chemicals or preservatives. Adjuvanted means it has a "booster". Unadjuvanted means it doesn't have a booster (it would take longer for the vaccine to take effect). One is not worse than the other.