Why did my 4th dose of rabies vaccine didn't hurt? my 1,2,3 doses hurt after some hours but 4th dose never hurted? why? they gave me the same vaccine.

Inflammatory respons: It's not unusual for the body to respond differently to subsequent doses of vaccine. In many cases, soreness actually increases with each dose, but sometimes people experience what you've described. However, it is certainly possible that the particular lot of vaccine you received for your 4th dose was less potent, less concentrated, or contained a slightly different set of ingredients.