Inclusion Criteria:  6 months ≤ Age of enrollment ≤71 months; Voluntary and self-funded completion of EV71 vaccine combined immunization with one of the other type I or II vaccines; The subject and/or guardian can understand and voluntarily sign the informed consent form; Subjects and their legal guardians are able to attend follow-up visits and follow all study procedures (such as cooperating in completing safety observation notes).  Exclusion Criteria:  -