There are many reasons for pus in the baby’s arm from vaccination: first, it may be normal, some vaccination, such as BCG, will gradually have pus after the vaccination, this is a normal phenomenon, do not need to pay special attention, they will slowly disappear. The second, may be the vaccination is not disinfected, or the vaccination after taking a shower, water into the eye of the needle is easy to bacterial infection, there is pus situation. The third, the staff injection vaccination method is not correct, not injected into the subcutaneous, only injected into the skin, this situation will also appear to have the symptoms of pus. The symptoms of pus in the vaccination, do not squeeze out the pus, first disinfection with iodine volts, if necessary, oral anti-inflammatory drugs, if there is no improvement, to go to the hospital in a timely manner.