Infants and children with fever at night after MMR vaccination should be observed, which is one of the adverse reactions after vaccination. Physical cooling is recommended for temperatures below 38.5 degrees Celsius, and antipyretics such as ibuprofen are recommended for temperatures above 38.5 degrees Celsius. MMR vaccine belongs to a kind of combined vaccine, equivalent to three kinds of antigenic substances inoculated into the human body at the same time, so it may produce adverse reactions, usually after the MMR vaccination may have a slight fever, this adverse reaction can be subsided with time, due to the antigenic stimulation of the immune system and produce. When fever occurs in the evening after MMR vaccination, if it is mild, parents should pay attention to observation and use physical cooling as appropriate, do not worry too much. If the temperature exceeds 38.5 degrees Celsius, it should be taken seriously, and fever-reducing medicines can be taken under the guidance of the doctor, and if necessary, go to the hospital for treatment, so as to avoid delaying the condition.