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.
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.