The presence of fever after the injection of the diphtheria vaccine indicates the beginning of an inflammatory reaction in the body. There are two possibilities for this inflammatory reaction: the first one may be a normal immune response, in which protective antibodies can be produced for later protection; the second one may be an allergic reaction. The normal inflammatory response is usually a body temperature over 38°C. If it reaches 39℃, the possibility of allergy is higher. If the patient also has chills and other symptoms, it is recommended that anti-allergy treatment is needed at the hospital.