For a one-year-old baby with fever after vaccination, if the fever is low, it does not need to be treated. If the temperature reaches 38°C or above, acetaminophen or ibuprofen can be given to improve the baby’s fever and emotional irritability. Vaccines are generally very safe, but they are not perfect. Like drugs, they can occasionally cause reactions in the body, and some children often have mild symptoms of illness the night after vaccination, such as low-grade fever and emotional irritability, as well as pain, redness, and swelling at the injection site. In very rare cases, the child’s reaction to the vaccine may be more severe, such as high fever and rash. If your child has a temperature of 39.5°C, a rash all over the body, including hives, edema in the limb that received the injection, or other symptoms, you should visit the pediatrician at the hospital.