The main purpose of this study is to evaluate the immunogenicity and safety of inactivated enterovirus type 71 vaccine combined with recombinant hepatitis B vaccine or Group a meningococcal polysaccharide vaccine.

This study conducts a randomized, controlled design, enrolled infants over 6 months old as the participant, and setting up three parallel groups. Participants are randomly assigned to three groups. The first group is the inactivated enterovirus type 71 Vaccine (EV71 vaccine), Recombinant hepatitis B vaccine and Group A meningococcal polysaccharide vaccine combined administration group. The first dose of inactivated EV71 vaccine and Recombinant hepatitis B vaccine are combined administration on day 0, and the second dose of inactivated EV71 vaccine and Group A meningococcal polysaccharide vaccine are combined administration on day 30. The second group is the inactivated EV71 vaccine single administration group, with two doses of inactivated EV71 vaccine administered on day 0 and day 30 respectively. The third group is Recombinant hepatitis B vaccine and Group A meningococcal polysaccharide vaccine administration group, the Recombinant hepatitis B vaccine is administered on day 0, and the Group A meningococcal polysaccharide vaccine is administered on day 30. Each participant will be followed up 30 minutes, 24 hours, 48 hours, and 72 hours after each vaccination actively, and will be reported for 4-30 days to collect adverse reactions/events passively. All participants collect serum samples before administration (day 0) and second dose of administration (day 30), 30 days and 1 year after full-term administration (day 60 and 1 year). The serum samples of participants will be collected 5 years after full-term administration at the first and second group. The immunogenicity of the inactivated EV71 vaccine, Recombinant hepatitis B vaccine, and Group A meningococcal polysaccharide vaccine of three groups participants will be detected and analyzed.

Inclusion Criteria:

• Healthy children aged 6-7 months with no history of vaccination within the past month and normal intelligence.
• Healthy individuals determined by researchers after inquiring about medical history and physical examination.
• The recipients are able to comply with the requirements of the research protocol and undergo immunogenicity testing.
• Individuals without contraindications.
• Underarm temperature ≤ 37 ℃.
• Obtain informed consent from the recipient's guardian and sign an informed consent form.

Exclusion Criteria:

• Individuals with any serious illness.
• Individuals who are allergic to any ingredient in the research vaccine.
• Individuals with a history of neurological symptoms or signs.
• Individuals with bleeding constitution or prolonged bleeding time.
• Individuals who have had hand, foot, and mouth disease, hepatitis B, and epidemic cerebrospinal meningitis in the past.
• Individuals who have received other vaccines or immunoglobulin injections or any investigational drugs within the past 4 weeks.
• Infected individuals who have had any acute illness or require systemic antibiotic or antiviral treatment within the past 7 days.
• Individuals who have experienced fever (axillary temperature ≥ 38 ℃) within the past 3 days.
• Participating in another researcher.
• Individuals with a history or family history of allergies, seizures, epilepsy, encephalopathy, and mental illness.
• Patients with thrombocytopenia or other coagulation disorders that may cause contraindications for intramuscular injection.
• Patients with severe chronic diseases.
• Known or suspected concurrent diseases include: respiratory system diseases, acute or chronic disease activity period, HIV infection in the mother or research subject of the child, cardiovascular disease, severe hypertension, malignant tumor treatment period, and skin disease patients.
• Endemic disease patients.
• Those who plan to leave their place of residence before the end of the study.
• Researchers believe that any situation that may affect observation and evaluation.