Fever in children on the second day after varicella vaccination is mainly due to the following conditions. First, due to the reaction of chickenpox vaccination, children will have an immune reaction after receiving chickenpox vaccine, and if the immune reaction is strong, it will cause fever in children, which is mostly low fever. Secondly, if the child has been vaccinated with chickenpox vaccine, after blowing cold or other improper care, it will often cause a low immunity, which will cause acute upper respiratory tract infection, then there will also be fever, nasal congestion, runny nose and other symptoms, you can drink more warm water, most of them will improve in 2-3 days.