Immunity and Safety of Inactivated Enterovirus 71 Vaccine Post-marketing Among Children Aged 6-35 Months in China

Inclusion Criteria: * Healthy children aged 6-35 months * Subjects who have been clinically judged to be healthy by the researcher after being asked about the medical history and related physical examination * The subjects' guardians agree the requirements of the protocol and the relevant follow up visits * The subjects' guardians agree and sign the informed consent * Subjects who have no relocation or long-term travel plan within one year and are able to comply with the requirements of the clinical trial protocol. Exclusion Criteria: * Subject who has a medical history of HFMD caused by EV71 or has been vaccinated with EV71 vaccine * Subject that has a history of allergies to vaccines or vaccine ingredients, and has serious side effects on vaccines, such as allergies, urticaria, dyspnea, vascular neuroedema or abdominal pain * Subject who has congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc. * Subject who has a history of epilepsy, convulsion or convulsion, or a family history of mental illness * Subject who has autoimmune disease or immune deficiency, or whose parents and siblings have autoimmune disease or immune deficiency * Subject who has a history of asthma, vascular and neuroedema, diabetes or malignant tumor * Subject who has a thyroid resection history, or received treatment due to thyroid disease in the past 12 months * Subject who has an abnormal coagulation function (such as coagulation factor deficiency, coagulant disease, platelet abnormality) or obvious bruising or clotting disorder which was diagnosed by doctors. * Asplenia, functional asplenia, or splenectomy due to any circumstances * Acute onset of various acute or chronic diseases in the last 7 days * Immunosuppressant therapy, antiallergic therapy, cytotoxicity therapy, inhaled corticosteroids (excluding corticosteroid spray therapy for allergic rhinitis, surface corticosteroid therapy for acute non-dermatitis) in the past 6 months * Any prior administration of blood products in last 3 months * Any prior administration of other research medicines or vaccines in last 1 month * Any prior administration of attenuated live vaccine in last 15 days * Any prior administration of subunit or inactivated vaccines in last 7 days * Under the anti-TB prevention or therapy * Underarm temperature \> 37.0 ℃ for fever before vaccination * Other factors that are not suitable for clinical trials according to the judgment of researchers Exclusion Criteria for the second dose: * Have severe allergic reaction after first dose * Have severe adverse reactions related to first dose * Any situation meet the exclusion criteria stated in the exclusion criteria for first dose * Acute infection or illness * Other factors that are not suitable for clinical trials according to the judgment of researchers