Bridging Clinical Trial of EV71 Vaccine in Vietnamese Children

Inclusion Criteria: * Healthy children aged 6\~71 months when receiving the first dose of investigational EV71 vaccine; * Participants' legal guardians are able to understand and sign the informed consent voluntarily; * Participants are able to comply with the study procedures based on the assessment of the investigator; * Participants should provide verifiable identification, be reachable by the investigator and must be able to contact the investigator throughout the study period. Exclusion Criteria: * Prior history of hand, foot and mouth disease (HFMD); * Have been exposed to a case with laboratory-confirmed (virological diagnosis, e.g., via PCR or virus isolation) HFMD at home, day care, or other settings within 2 weeks before enrollment; * Prior participated in clinical trial of EV71 vaccine and received any investigational EV71 vaccine; * Known allergy to vaccines or vaccine ingredients, or serious adverse reactions to vaccines, such as urticaria, dyspnea, angioneurotic edema; * Any known or history of autoimmune diseases (including but not limited to systemic lupus erythematosus, rheumatoid arthritis, etc.) or immunodeficiency/immunosuppression (such as HIV infection, organ transplantation), asplenia; * Received immunosuppressive for ≥14 days (e.g., prednisone equivalent of ≥2 mg/kg), or cytotoxic drug before enrollment, or plans to receive these treatments during the study participation. * Receipt of blood products or immunoglobulins within the past 3 months before enrollment in this study, or scheduled to receive these treatments during the study period; * Receipt of other investigational vaccines within 30 days prior to vaccination in this study; * Receipt of other vaccines within 14 days prior to vaccination in this study; * Presence of any acute disease (moderate to severe illness, with or without fever) or an acute exacerbation of a chronic condition within the 7 days prior to vaccination in this study. * Has fever on the day of vaccination, with the axillary temperature ≥ 37.5 celsius before vaccination; * Is participating in or planning to participate in other vaccine or drug clinical trials; * According to the investigator's judgment, the participant has any other factors that might interfere with the clinical trial results or pose additional risk to the participant due to participation in the study.