There is no need to be nervous if you have a fever after a diphtheria vaccination. If the fever is only low and there are no clinical symptoms, it is mainly important to hydrate properly, drink more warm water, and wear looser, sweat-absorbing cotton clothes to facilitate sweating, heat dissipation, and fever reduction. If the fever is high or accompanied by clinical symptoms, such as cough, nasal congestion, runny nose, vomiting, diarrhea and abdominal distension, usually secondary viral or bacterial infections should be considered, then take antipyretic drugs, such as ibuprofen, when the fever is high, and low fever can be assisted by physical cooling methods, such as applying cooling patches, etc. At the same time, you should take your child to the hospital for a review, which requires blood tests and C-reactive protein to assess the status of the infection. If the infection is only viral, symptomatic treatment is usually sufficient, while if there is a bacterial infection, you should choose the appropriate antibiotics to fight the infection according to the child’s clinical symptoms.