The purpose of this study is to evaluate the immunogenicity and safety of sequential vaccination of two EV71 inactived vaccines in healthy infants aged 6-35 months.

This study is a opened,randomized and controlled phase Ⅳ clinical trial. The purpose of this study is to evaluate the immunogenicity and safety of sequential vaccination of two EV71 inactived vaccines in healthy infants aged 6-35 months. EV71 inactived vaccines(Vero cells）was manufactured by Sinovac Biotech Co., Ltd and EV71 inactived vaccines(Human diploid cells）was manufactured by Institute of Medical Biology Chinese Academy of Medical Sciences.300 infants aged between 6-35 months will be randomly assigned into experimental group in the ratio 1:1:1:1.The experimental group 1 received two doses EV71 inactived vaccines(Vero cells）on day 0 and 30. The experimental group 2 received two doses EV71 inactived vaccines (Human diploid cells）on day 0 and 30. The experimental group 3 received one dose EV71 inactived vaccines (Vero cells）on day 0 and one dose EV71 inactived vaccines (Human diploid cells）on day 30.The experimental group 4 received one dose EV71 inactived vaccines (Human diploid cells）on day 0 and one dose EV71 inactived vaccines (Vero cells）on day 30. To evaluate the immunogenicity of the vaccine, venous blood will be collected for the EV71 neutralizing antibody detection prior to vaccination and 30 days after the 2nd dose vaccination.

Inclusion Criteria:

• Healthy volunteer aged 6-35 months;
• Proven legal identity;
• Guardians of the participants should be capable of understanding the written consent form, and such form should be signed before the infant being included into this study.

Exclusion Criteria:

• Prior vaccination with EV71 vaccine;

• History of hand，foot and mouth disease;

• Allergy to gentamicin; history of allergy to any vaccine or vaccine ingredient, or serious adverse reaction(s) to vaccination, such as urticaria,difficulty in breathing, angioneurotic edema, pain, etc;

• Congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc;

• Autoimmune diseases or immunodeficiency/immunosuppression;

• Severe neurological disorders (epilepsy, convulsions or convulsions) or psychosis;

• History of thyroidectomy, absence of spleen, functional absence of spleen, and any circumstances leading to absence of spleen or splenectomy;

• Diagnosed coagulation function abnormal (e.g., coagulation factor deficiency, coagulation disorder, or platelet abnormalities) , or obvious bruising or coagulation disorders;

• Any immunosuppressant, cytotoxic medicine, or inhaled corticosteroids (except corticosteroid spray for treatment of allergic rhinitis or corticosteroid treatment on surface for acute non-complicated dermatitis) in the past 6 months;

• Receipt of any of the following products:

  1. Blood product within 3 months prior to study entry;
  2. Any live attenuated vaccine within 14 days prior to study entry;
  3. Any subunit vaccine or inactivated vaccine within 7 days prior to study entry;
  4. Any other study drugs within 30 days prior to study entry;

• Acute disease or acute stage of chronic disease within 7 days prior to study entry;

• Axillary temperature > 37.0℃;

• Any other factor that suggesting the volunteer is unsuitable for this study based on the opinions of investigators.