This multicenter, randomized, double-blind, controlled Phase III clinical trial aims to evaluate the efficacy, safety, and immunogenicity of the bivalent enterovirus-inactivated vaccine (Vero cell) in healthy children aged 6 to 71 months.
The main questions it aims to answer are:
* The primary vaccine efficacy of the investigational vaccine against Hand, Foot, and Mouth Disease（HFMD) caused by CA16 infection compared to the control vaccine. * The neutralizing antibody levels against EV71 in the trial group are non-inferior to those in the control group after two doses of vaccination.
Researchers will compare the bivalent enterovirus-inactivated vaccine (Vero cell) to the EV71-inactivated vaccine (Vero cell) to prevent HFMD and Herpangina(HA).
Participants will be randomly assigned to the trial group and the control group in a 1:1 ratio to receive two doses of the investigational vaccine or the control EV71 vaccine, with a one-month interval between doses.
Healthy children aged 6 to 71 months with no history of EV71 vaccination; or healthy children aged 24 to 71 months who have completed two doses of EV71 vaccine at least 6 months prior.
Guardians who can understand and voluntarily sign the informed consent form.
Willing and able to comply with all visit schedules, sample collections, vaccinations, and other research procedures.
Provide proof of identity documents.
A known history of HFMD/HA.
Uncontrolled chronic diseases or a history of severe illnesses, including but not limited to cardiovascular diseases, blood disorders, liver or kidney diseases, digestive system diseases, respiratory system diseases, malignant tumors, or a history of major functional organ transplantation.
Autoimmune diseases, immunodeficiency diseases (including but not limited to systemic lupus erythematosus, ankylosing spondylitis, autoimmune thyroid diseases, asplenia, functional asplenia, and HIV infection).
Abnormal coagulation function (such as coagulation factor deficiencies, and platelet abnormalities).