When a child has a fever two days after vaccination, this is mainly due to the following reasons: First, due to the immune response to the vaccination, some children will have a strong immune response after vaccination, which can cause fever, the fever at this time is often not particularly high, rarely more than 39 ℃ under the armpit. Children can be given more rest and warm water. Secondly, children who happen to be suffering from other infections, such as respiratory or digestive tract infections after vaccination, if they are not well taken care of in a timely manner, or after being exposed to wind, cold or improper diet, may also cause fever, which requires timely treatment of respiratory tract infections and digestive tract infections.