There must be a problem that the fever does not go away after vaccination, suggesting that the child has a secondary bacterial or viral infection, because some children will have an immune reaction after vaccination and may have a low fever reaction within 24h, which is usually not accompanied by other clinical symptoms and does not require special treatment, so just pay attention to drinking more water appropriately. However, some children are highly sensitive and have lowered resistance after vaccination, and are prone to viral and bacterial infections, causing a high fever with an axillary surface temperature >38.5°C. If this fever continues repeatedly for more than 24h, then there must be a problem. It may lead to serious infection or aggravation of the condition, and may even affect the effectiveness of vaccination, so it is important to go to the hospital promptly to check the cause and treat the cause. If it is a viral infection it is usually treated symptomatically, and if there is a basis for a bacterial infection it usually requires oral or intravenous antibiotic treatment.