There is no specific rule about how long the second dose of HFMD vaccine can be delayed at most, but it is generally recommended that the vaccination should not be given beyond 1 week of age. HFMD is a common infectious disease in children caused by enteroviruses and is most common in children between the ages of 6 months and up to 5 years. The HFMD vaccine mainly targets enterovirus 71, which can cause severe HFMD. In addition, because the immune system of infants and young children is not fully developed, the younger the child, the greater the chance of contracting severe HFMD. Therefore, the earlier the second dose of HFMD vaccine is given after the first month of vaccination, the stronger the immunization effect and the better the protection for the child. For HFMD, parents are advised to let their children develop good habits of hygiene, wash their hands before meals and not drink raw water. In addition, children also need to pay attention to strengthen physical exercise, try to achieve a balanced diet, in order to improve their own resistance.