The second dose of MMR vaccine will cause fever in some but not in most vaccinated persons, but if fever occurs with the first dose, there is a higher chance of fever with the second dose. MMR vaccine is a preventive vaccine preparation against measles, rubella and mumps, which is a class I vaccine within the national policy. It is usually required to be administered to children between 1 and 14 years of age, with a total of two injections, and some of the children will have a febrile reaction, commonly known as a fever, after the first and second injections. Some children will have a febrile reaction, commonly known as a fever, after the first and second injections. If the fever is present during the first injection, it is more likely to be present during the second injection. If the fever is only low after vaccination, no special treatment is needed, and the child will recover on his/her own after a few hours, or you can use a wet towel to apply a cold compress to the forehead to speed up the recovery of the body temperature. If you have a high fever after vaccination, report it to your doctor and undergo an examination to determine whether it is a reaction to the vaccine or caused by other reasons, so that appropriate measures can be taken. It is important to note that the MMR vaccine should be used under the guidance of a physician and should not be injected blindly on one’s own.