The reaction after the second injection of MMR vaccine will be relatively small, as long as no allergic reaction occurs then there is no need to worry too much. The MMR vaccine is an attenuated MMR virus, which can be used to prevent measles, mumps and rubella, and the reproduction of the virus in the body will reach its peak in about 7 days after the first vaccination, and the antibodies produced in the body will also reach its peak, and at this time, the inoculated person will usually have fever, rash and other conditions. Compared with the first vaccination, the reaction of the second MMR vaccination will be significantly reduced, at this time, the body has already produced antibodies, and a large number of antibodies will be produced about three days after the second vaccination, and the reproduction of the MMR virus will be gradually reduced, and at this time, as long as there is no allergy, there will not be any other adverse reactions. It is recommended to go to regular hospitals for vaccination to avoid the occurrence of adverse reactions.