New vaccine aims to shield kids from hand, foot, and mouth disease

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Healthy participants aged 18-59 years (only applicable for Phase I) or 6 months to 12 years. * Participants and/or their legal guardians are able to understand and voluntarily sign the informed consent form (for participants aged 8-12, both the participant and their guardian must sign). * Willing and able to comply with all visit schedules, sample collection, vaccinations, and other trial procedures, and maintain contact during the trial period. * Provide identification for the participant and/or their guardian. * Participants of childbearing participants and their sexual partners must voluntarily use effective contraceptive measures from the time of signing the informed consent form until three months after the completion of the two-dose vaccination series with the investigational vaccine, and have no plans to donate sperm or ova (only applicable for Phase I participants aged 18-59 years). Exclusion Criteria: * History of HFMD or HA (only applicable to Phase II clinical trial participants). * Presence of uncontrolled chronic diseases or history of serious illnesses, including but not limited to cardiovascular diseases, hematological diseases, liver and kidney diseases, digestive system diseases, respiratory diseases, malignant tumors, and history of major organ transplantation. * Severe congenital malformations, genetic defects, or malnutrition. * Presence of autoimmune diseases or immunodeficiency diseases (including but not limited to systemic lupus erythematosus, ankylosing spondylitis, autoimmune thyroid diseases, asplenia, functional asplenia, HIV infection). * Abnormal coagulation function (such as coagulation factor deficiency, platelet abnormalities). * Suffering from/having suffered from severe neurological diseases (epilepsy, convulsions, or seizures \[excluding febrile convulsions\]), mental illness, or having a family history of mental illness. * Acute illnesses or acute exacerbations of chronic illnesses within the past 3 days. * Having been vaccinated with a vaccine containing any of the components EV71, CA16, CA10, CA6 (including marketed vaccines or investigational vaccines). * Having received ≥14 days of immunosuppressive or other immunomodulatory treatment (adults: prednisone ≥20mg/day, or children: ≥2mg/kg/day, or equivalent doses; excluding topical or inhaled corticosteroids) within the past 6 months, or cytotoxic treatment, or planning to receive such treatment during the trial. * Having received immunoglobulins or other blood products within the past 6 months, or planning to receive such treatment during the trial. * Having received other investigational drugs or vaccines within the past 30 days, or planning to receive such drugs or vaccines during the trial. * Having received live attenuated vaccines or nucleic acid vaccines within the past 14 days, or subunit or inactivated vaccines within the past 7 days. * Known allergy to any component of the investigational vaccine (inactivated EV71, CA16, CA10, and CA6 viruses, aluminum hydroxide adjuvant, disodium phosphate, sodium dihydrogen phosphate, sodium chloride, water for injection). * Participants who are breastfeeding, pregnant, or planning to become pregnant within 3 months after the two doses of vaccination in this trial (only applicable to Phase I). * On the day of planned vaccination with the investigational vaccine, having an axillary temperature \>37.0°C before vaccination, or other vital sign measurements outside the normal range. * Failing the physical examination on the day of planned vaccination with the investigational vaccine. * Clinically significant laboratory abnormalities beyond the reference range in clinical laboratory tests (only applicable to Phase I clinical trial participants): 1. Hematology-related test indicators (adults aged 18-59 and children aged 6- white blood cell count, hemoglobin, and platelet count. 2. Blood chemistry-related test indicators (adults aged 18-59, children aged 6-12, and children aged 24-71 months): alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), fasting blood glucose. 3. Urinalysis-related test indicators (adults aged 18-59 and children aged 6-12): urine protein (PRO). * Presence of skin lesions, inflammation, ulcers, rashes, scars, or other conditions at the intended injection site that may interfere with vaccination or observation of local reactions. * Any other factors deemed by the investigator to make the participant unsuitable for participation in the clinical trial.