An Immunity Persistence Study of Enterovirus 71 Inactivated Vaccine (Vero Cell)

An Open, Observational Study to Evaluate the Immunity Persistence of an Inactivated Enterovirus 71 Vaccine (Vero Cell) in Subjects Aged 6 to 71 Months

This is an open，observational and follow-up clinical trial based on the clinical trial of EV71 vaccine extended age group.The purpose of this study is to evaluate the immunity persistence of EV71 vaccine developed by Sinovac Biotech Co., Ltd in subjects aged 6 ~71 months after full immunization of two doses of vaccine.

This study is an open,observational and follow-up clinical trial of EV71 vaccine based on the clinical trial of EV71 vaccine extended age group.The main purpose of this study is to evaluate the immunity persistence of EV71 vaccine developed by Sinovac Biotech Co., Ltd in subjects aged 6~71 months after full immunization of two doses of vaccine.In this study, a total of 474 subjects from the EV71 vaccine extended age clinical trial who received two doses of experimental or control vaccine and were enrolled in the PPS set，including 274 subjects aged 6~35 months (the maximum number of subjects aged 6-23 months is 146, and the maximum number of subjects aged 24-35 months is 128),100 subjects aged 36~71 months and were enrolled in experimental group(EV71 vaccine developed by Sinovac Biotech Co., Ltd) and 100 subjects aged 36~71 months and were enrolled in control group(EV71 vaccine developed by Institute of Medical Biology,Chinese Academy of Medical Sciences) will be enrolled .Blood samples will be collected from subjects aged 6-23 months at 36 months after full immunization and at the age of 72 months.Blood samples will be collected from subjects aged 24 to 35 months at 36 months after full immunization.Blood samples will be collected from subjects aged 36-71 months at 36 months after the full immunization.

Up to 146 subjects aged 6~23 months and have received EV71 vaccine developed by Sinovac Biotech Co., Ltd will be collected blood samples at 36 months after full immunization and at the age of 72 months.

Up to 128 subjects aged 24~35 months and have received EV71 vaccine developed by Sinovac Biotech Co., Ltd will be collected blood samples at 36 months after full immunization .

100 subjects aged 36~71 months and have received EV71 vaccine developed by Sinovac Biotech Co., Ltd will be collected blood samples at 36 months after full immunization .

100 subjects aged 36~71 months and have received EV71 vaccine developed by Institute of Medical Biology,Chinese Academy of Medical Sciences will be collected blood samples at 36 months after full immunization .

The EV71 vaccine was manufactured by Sinovac Biotech Co., Ltd and inactivated EV71 virus antigen was no less than 3.0EU in 0.5 mL of aluminium hydroxide solution per injection.

The EV71 vaccine was manufactured by Institute of Medical Biology,Chinese Academy of Medical Sciences ,and inactivated EV71 virus antigen was no less than 3.0EU in 0.5 mL of aluminium hydroxide solution per injection.

The seroconversion rates (SCR) of EV71 neutralizing antibody of all subjects at 36 months after full immunization.

The seroconversion rates (SCR) of the EV71 neutralizing antibody of subjects aged 6-23 months at the age of 72months.

Inclusion Criteria: Subjects in the EV71 vaccine extended age clinical trial who received two doses of experimental or control vaccine and were enrolled in the PPS set; Provide legal identification; Participants or guardians of the participants should be capable of understanding the written consent form and voluntarily participate in the clinical trial. Exclusion Criteria: Vaccination history of vaccines containing EV71 antigen components other than the EV71 vaccine expanded age group clinical trial; History of hand, foot and mouth disease caused EV71; According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.