Safety, Three Batches Consistency and Immunity Duration of the Post-marketing Inactivated Enterovirus Type 71 (EV71) Vaccine in Children Aged 6-71 Months

This study evaluates the safety,three batches consistency and immunity duration of the post-marketing inactivated Enterovirus Type 71 (EV71) vaccine in children aged 6-71 months.This study has two groups:safety observation group and immunogenicity observation group.20000 subjects will receive 2 doses vaccines and be observed for safety among 2 epidemic cycles of HFMD.In the immunogenicity observation group, 900 subjects will be randomly received 3 batches vaccines(2 doses),and blood sampled at days 0 and 56.