Efficacy Trial of a Commercial EV71 Vaccine

Inclusion Criteria: * Volunteers aged 6-71 months; * Guardians of the participants voluntarily to vaccinate the participants with EV71 vaccine at their own expense; * Guardians of the participants should be capable of understanding the written consent form, and such form should be signed prior to enrollment; * Complying with the requirement of the study protocol; Exclusion Criteria: * History of HFMD prior to the study entry; * Prior vaccination with EV71 vaccine; * History of allergy to any vaccine, or any ingredient, excipients and Gentamycin Sulfate of the vaccine, or serious adverse reaction(s) to vaccination, such as urticaria, dyspnea, angioneurotic edema, abdominal pain, etc. (only for 6-35 months old subjects of the vaccinated group) ; * Congenital malformation, developmental disorders, genetic defects, or severe malnutrition (only for 6-35 months old subjects of the vaccinated group); * Severe/uncontrollable nervous system disease (epilepsy, seizures or convulsions) or mental illness (only for 6-35 months old subjects of the vaccinated group); * Autoimmune disease or immunodeficiency/immunosuppressive (only for 6-35 months old subjects of the vaccinated group) ; * History of asthma, angioedema, diabetes or malignancy (only for 6-35 months old subjects of the vaccinated group); * Acute disease or acute stage of chronic disease within 7 days prior to study entry (only for 6-35 months old subjects of the vaccinated group); * Axillary temperature \> 37.0 Celsius (only for 6-35 months old subjects of the vaccinated group)； * Any other factor that suggesting the volunteer is unsuitable for this study based on the opinions of investigators.