Many small children may have fever after vaccination, not only after hepatitis B vaccination, but also after other vaccinations, which is actually a normal reaction of children after vaccination. After the vaccine is injected into the child’s body, the body will be mobilized to generate an immune response and produce antibodies, during which the baby may develop fever, often within 24 hours after vaccination and lasting no longer than 48 hours, and the temperature will not be particularly high, generally not exceeding 38.5°C. If your baby develops fever in the above situation after vaccination, parents can not worry too much and can help your child reduce the fever by physical cooling and, if necessary, by taking oral antipyretics. In addition, it is necessary to closely observe the baby’s mental state, the height and duration of the body temperature. If the temperature drops to normal within 48 hours and the child does not have any other reaction, it is a normal reaction to fever after vaccination. If a child develops high fever, poor mental health, or other symptoms such as coughing, vomiting, or diarrhea after vaccination, parents are advised to take the child to the hospital for prompt medical attention to avoid the child developing fever in combination with other infections during the vaccination process. In case of fever caused by other infections in combination with vaccination, different treatments are needed for different causes.