Herpes zoster is caused by the reactivation of latent varicella-zoster virus (VZV) which stays in latency after its primary infection. Immunosenescence contributes significantly to elevating morbidity associated with aging. Vaccination plays a key role in reducing the disease burden of zoster and the associated complications. We are conducting a study entitled "A Randomized, Blinded, Placebo- and Active-Controlled, Adaptive Phase 2 Clinical Trial to Evaluate the Immunogenicity and Safety of SYS6017 (a Herpes Zoster mRNA Vaccine) in Healthy Participants Aged 40 Years and Above".

Inclusion Criteria:

• 1. Individuals aged 40 years or older;
• 2. Able to understand the study procedures, comply with the protocol requirements to attend all the scheduled visits, voluntarily consent to participate in the study, and sign the informed consent form;
• 3. Is physically eligible at the discretion of investigators based on medical history inquiry and physical examination; For participants with chronic underlying diseases (e.g., diabetes mellitus, hypertension, hyperlipidemia and other chronic conditions), they may be enrolled if their conditions have been well controlled within 3 months prior to enrollment in this study (i.e., additional medical interventions or major adjustments to treatments are not required);
• 4. For female participants of childbearing potential: No sexual activity or effective contraceptive methods were used within one menstrual cycle before enrollment; No pregnancy plans and agree to adopt effective contraceptive methods within 8 months after enrollment.

Exclusion Criteria:

• 1. History of zoster;
• 2. History of vaccination with varicella vaccine or zoster vaccine (including investigational vaccine);
• 3. Axillary temperature ≥ 37.1℃ on the day of enrollment or within 24 h before enrollment;
• 4. History of allergy to any component of the investigational vaccine; or history of severe allergic reactions to vaccines or medications (including but not limited to anaphylaxis, allergic laryngeal edema, Henoch-Schönlein purpura, thrombocytopenic purpura, or Arthus reaction);
• 5. History of myocarditis, pericarditis, or idiopathic cardiomyopathy, or any condition that could increases the risk of myocarditis or pericarditis
• 6. History of demyelinating diseases, including but not limited to Guillain-Barré syndrome, multiple sclerosis, ophthalmoneuromyelitis, acute disseminated encephalomyelitis, etc.;
• 7. Current epilepsy or convulsion, severe neurological or psychiatric disorders;
• 8. Have contraindications to intramuscular injection, e.g., diagnosed thrombocytopenia, any coagulation disorders, or ongoing treatment with anticoagulants, etc.;
• 9. Active malignant tumor, malignant tumor without adequate treatment, malignant tumor with a potential risk of recurrence during the study;
• 10. Active, unstable, severe or uncontrolled cardiovascular and cerebrovascular diseases, thrombotic diseases, blood and lymphatic system diseases, liver and kidney diseases, respiratory diseases, metabolic diseases, musculoskeletal diseases, autoimmune diseases, etc;
• 11. History of diagnosed immunocompromise or immunosuppression, congenital or functional asplenia, or splenectomy before enrollment;
• 12. Long-term (defined as more than 14 consecutive days) systemic use of immunosuppressants, immunostimulants, or other immunomodulatory drugs (e.g., corticosteroids at a dose of ≥ 20 mg/day prednisone or equivalent) within 6 months prior to enrollment; however, inhaled and topical corticosteroids are permitted; or planned administration of the aforementioned agents during the study period;
• 13. Administration of whole blood, plasma, serum, immunoglobulin, or monoclonal antibodies within 3 months prior to enrollment, or planned administration of the aforementioned products during the study period;
• 14. Blood donation or blood loss ≥ 450 mL within one month before enrollment, or planning to donate blood during the study;
• 15. Vaccination with any other vaccines within 30 days prior to enrollment, or planned vaccination with any other vaccines within 30 days after the last dose of the study vaccine;
• 16. Current participation in or planned participation in other clinical trials during the study period;
• 17. For female participants of childbearing potential: positive pregnancy test result prior to enrollment, current pregnancy or lactation, or planned pregnancy within 8 months after enrollment;
• 18. Unable to comply with the study procedures and requirements, or presence of other conditions that make the participant inappropriate for this clinical trial, as judged by the investigators.