The purpose of this study is to elucidate the molecular mechanism by which novel adjuvants enhance the immunogenicity of Respiratory Syncytial Virus (RSV) vaccines by regulating antigen-specific B cell affinity maturation and T cell memory formation.

Novel adjuvants can effectively induce humoral immunity and generate neutralizing antibodies, as well as activate cellular immunity to clear intracellular pathogens.They mainly include particle-based adjuvants based on molecular agonists, synthetic inorganic/organic particulate materials, and virus-like particle mimetics.This study focuses on the mechanisms by which adjuvants enhance humoral and cellular immunity, analyzes antibody lineages, structural characteristics, and the patterns of T-cell activation, differentiation and memory formation, and elucidates the regulatory effects of adjuvants on antibody breadth and neutralizing activity. This study aims to systematically study the role of RSV adjuvants in enhancing high-affinity antibody responses and CD4⁺/CD8⁺ memory T cell generation through multi-dimensional immune analysis methods, including B Cell Receptor (BCR) / T Cell Receptor (TCR) sequencing, flow cytometry, and single-cell omics, so as to provide theoretical basis and new ideas for improving the sustainability and broad-spectrum immunization effect of novel RSV vaccines. A total of 60 adults aged 20 years and above will be enrolled. All participants will receive a single dose of investigational vaccine.

Inclusion Criteria:

• Participants must be 20 years of age or older as determined by the investigator at enrollment.

• Participants must be able to understand study procedures, risks, and benefits, provide voluntary agreement to participate in the study, and sign the informed consent form (ICF).

• Participants must be willing and able to attend all scheduled follow-up visits and comply with all requirements specified in the study protocol.

• Females of childbearing potential must use highly effective contraception from 1 month prior to vaccination through 12 months following vaccination.

  • Effective contraceptive methods include: oral contraceptives (excluding emergency contraceptives), contraceptive injections, subcutaneous implants, hormonal patches, intrauterine devices (IUDs), surgical sterilization, true abstinence, and condom use.
  • Methods not considered effective include: rhythm method, withdrawal method, and emergency contraception.

Exclusion Criteria:

*Participants who meet any of the following criteria shall be ineligible for enrollment:

• Axillary body temperature ≥ 37.3 °C.
• History of respiratory syncytial virus (RSV) infection within 6 months prior to enrollment.
• New-onset respiratory infection symptoms within 7 days prior to enrollment, including cough, expectoration, dyspnea, wheezing, fever, rhinorrhea, and nasal obstruction.
• Presence of an acute illness or acute exacerbation of a chronic condition within 3 days prior to enrollment.
• Use of antipyretics and analgesics (excluding enteric-coated aspirin for the prevention of cardiovascular and cerebrovascular diseases) or antiallergic medications within 3 days prior to enrollment.
• Known hypersensitivity to any ingredient of the study vaccine, including Quillaja saponaria (QS-21), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), cholesterol, sucrose, sodium dihydrogen phosphate, anhydrous disodium hydrogen phosphate, polysorbate 80, sodium chloride, hydrochloric acid, and sodium hydroxide; history of severe allergic reactions or serious adverse events following any vaccination or drug administration, including anaphylactic shock, allergic laryngeal edema, allergic purpura, thrombocytopenic purpura, local Arthus reaction, and severe urticaria.
• Pregnant female (positive urine pregnancy test), lactating female, or female with a pregnancy plan within 12 months following vaccination.
• Congenital asplenia, functional asplenia, or splenectomy due to any cause.
• Previous or current malignant neoplasm, with the exception of clinically cured carcinoma in situ and papillary thyroid carcinoma.
• Confirmed diagnosis of an autoimmune disease, including systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, and autoimmune thyroid disease.
• Confirmed or suspected immunosuppression or immunodeficiency resulting from any cause, including primary or secondary immunocompromise, congenital or acquired immunodeficiency, human immunodeficiency virus (HIV) infection, or treatment with immunosuppressive or cytotoxic agents (e.g., chemotherapy, organ transplantation, or therapy for autoimmune diseases).
• Any condition that, in the investigator's judgment, would render intramuscular injection unsafe, such as a history of thrombocytopenia or other coagulation disorders.
• Previous or current serious clinical illness that is not cured (such as serious cardiovascular and cerebrovascular diseases, liver and kidney diseases, respiratory diseases, diabetes with complications, major surgery, etc.) may affect the evaluation of the trial.
• Previous or current thrombotic diseases.
• History of untreated tuberculosis or active tuberculosis infection at enrollment.
• Uncontrolled hypertension defined as systolic blood pressure ≥ 150 mmHg and/or diastolic blood pressure ≥ 100 mmHg on measurement prior to vaccination.
• History of severe cardiac arrhythmia (e.g., atrial fibrillation).
• History or family history of convulsions, epilepsy, congenital brain malformation, psychiatric disorders, or other severe neurological conditions associated with cerebral nerve tissue injury, including brain tumor, cerebral hemorrhage, cerebral infarction (excluding lacunar cerebral infarction and cerebral infarction without sequelae), central nervous system infection, and chemical intoxication.
• History of any cognitive disorder or any moderate or severe condition causing cognitive impairment.
• Use of any investigational or unlicensed product (medicinal product, vaccine, or medical device) other than the study vaccine within 30 days prior to vaccination, or planned participation in another clinical trial during the study period.
• Administration of any inactivated vaccine within 14 days prior to vaccination, or any live vaccine within 28 days prior to vaccination.
• Prior receipt of any RSV vaccine.
• Administration of immunoglobulin and/or any blood or plasma derivative (e.g., gamma globulin, intravenous immunoglobulin) within 3 months prior to vaccination, or planned administration during the study period.
• Long-term use (consecutive use > 14 days) of immunosuppressive or other immunomodulatory agents within 3 months prior to vaccination or planned use during the study period. Systemic glucocorticoids ≥ 20 mg prednisone or equivalent daily for ≥ 14 days are considered long-term use. Topical preparations (ointments, eye drops, inhalations, nasal sprays) at doses not exceeding those recommended in the package insert are permitted.
• Use of long-acting immunomodulatory agents (e.g., infliximab) within 6 months prior to vaccination or planned use during the study period.
• History of chronic alcohol abuse and/or drug abuse that, in the investigator's judgment, may interfere with study assessments.
• Planned migration during the study period that would preclude completion of all study procedures.
• Any other condition that, in the investigator's judgment, may interfere with the validity of study evaluations, with special attention to respiratory infection symptoms.