Fever in babies the day after vaccination is often an adverse reaction to the vaccine, which is also relatively normal. Some children may have a mild fever after vaccination, so pay attention to monitoring the body temperature and drink more water, and the temperature will come down in 2-3 days. Because vaccines are mostly inactivated bacteria or viruses, or possibly toxoids, these substances can stimulate the thermoregulatory center and cause certain abnormalities in the body temperature adjustment point, so there will be an increase in body temperature, resulting in fever, which is usually not particularly serious, and the temperature of the fever is not particularly high, and the duration of the fever is not particularly long, usually 2-3 days can be back to normal. However, some children’s body temperature will be higher, the first thing to do at this time to reduce the fever treatment, otherwise it is easy to occur the phenomenon of high fever convulsions, the child’s brain cells or brain function damage, it is recommended to take oral ibuprofen suspension.