A Study to Evaluate Efficacy, Immunogenicity and Safety of a Recombinant Respiratory Syncytial Virus Vaccine in Older Adults Aged 60 Years and Older

Inclusion Criteria:

• A male or female participant aged 60 years and above；
• Participants can provide valid identification, voluntarily agree to participate in the study, and sign the Informed Consent Form, and are able to attend all planned follow-up visits and comply with the protocol requirements；
• Axillary temperature ≤ 37.0°C on the day of enrollment;
• Female participants should have been menopausal or have undergone sterilization surgery; Menopause is defined as the absence of menstruation for at least 12 consecutive months without alternative medical measures; sterilization surgeries include bilateral tubal ligation or bilateral oophorectomy or hysterectomy; Male participants must not plan to father a child from the time of screening until 30 days after vaccination;
• Participants in the trial who were judged by the researchers to be healthy or have stable health conditions. [Stable health condition: This refers to having a chronic disease and maintaining a stable condition within the three months prior to enrollment irrespective of receipt of specific treatment, such as diabetes, hypertension, chronic obstructive pulmonary disease, and asthma. If the researcher determines that the condition is stable, participation in this trial will be permitted.].

Exclusion Criteria:

• Participants who are known to be allergic to any of the components contained in the test vaccine (e.g., sucrose, polysorbate 20, sodium dihydrogen phosphate dihydrate, and disodium hydrogen phosphate dihydrate.); A history of severe allergic reactions or serious adverse reactions to any vaccine;
• A confirmed diagnosis or etiological evidence of respiratory syncytial virus infection and related diseases caused by the infection within 12 months before enrollment (confirmed by RT-PCR, RSV-Ab, etc.);
• Have received or plan to receive any marketed or experimental RSV vaccine/RSV prophylactic medication;
• Has taken antipyretics, analgesics (except for medications used for underlying conditions that, in the investigator's judgment, are unlikely to affect study outcomes, such as enteric-coated aspirin for the prevention of cardiovascular and cerebrovascular diseases.) or anti-allergy drugs within 3 days before enrollment;
• Receipt of any non-live vaccine within 14 days prior to enrollment, or any live or nucleic acid vaccine within 28 days prior to enrollment;
• Any non-specific immunoglobulins and/or blood products containing non-specific immunoglobulins (such as whole blood, plasma) have been used within 3 months prior to enrollment or are planned to be used during the trial;
• Individual with the following diseases: ①Has acute diseases or are in the acute exacerbation period of chronic diseases within 3 days before vaccination; ②Individual with active tuberculosis or currently undergoing treatment for tuberculosis; ③History of congenital or acquired immunodeficiency or autoimmune diseases; Chronic administration (≥14 consecutive days) of corticosteroids (dose ≥ 20 mg/day prednisone or equivalent dose) or other immunomodulatory medications within the past 3 months, currently using or planning to use a long-acting immunomodulatory agent (e.g., infliximab), with the exception of inhaled or topical steroids, or short-term use (<14 consecutive days) of oral corticosteroids; ④Previous or current neurological disorders resulting in damage to brain nervous tissue (including seizures [specifically excluding simple febrile seizures in children], encephalopathy, etc.); or uncontrolled epilepsy with seizures occurring within 1 year prior to enrollment; or a history of psychotic disorders that affect normal behavior; ⑤Asplenia or functional asplenia; ⑥ Any cardiovascular, respiratory, hepatic, renal, metabolic, hematologic, or lymphatic disease deemed by the investigator to be unstable or uncontrolled (defined as requiring a major adjustment in treatment regimen within 3 months prior to enrollment, or hospitalization due to disease worsening; Individual with a history of lacunar cerebral infarction or cerebral infarction without residual sequelae can be enrolled if, after careful evaluation by the investigator, the condition has remained stable without recurrence for at least 5 years prior to enrollment); Individual with active malignancy or currently receiving antineoplastic therapy (excluding adjuvant endocrine therapy) are excluded (Certain malignancies, such as carcinoma in situ that has been clinically cured or papillary thyroid carcinoma, can be permitted following careful investigator assessment if there is no evidence of recurrence for ≥5 years prior to enrollment); ⑦Coagulation disorders (e.g., hemophilia or platelet count < 50 × 10⁹/L) that are contraindications for intramuscular injection; ⑧Uncontrolled hypertension as determined by the investigator (measured on-site: systolic blood pressure ≥ 160 mmHg and/or diastolic blood pressure ≥ 100 mmHg whether or not receiving medication); ⑨Arrhythmias that are newly diagnosed within 3 months prior to enrollment, not adequately controlled, or have required modification of treatment within 3 months prior to enrollment;
• Oxygen saturation (SpO₂) ≤ 90% as measured on site;
• History of major surgery within 6 months prior to enrollment (as determined by the investigator), or not fully recovered from the surgery, or having plans for major surgery during the study;
• A history of alcohol consumption and/or drug abuse that, in the investigator's judgment, may affect study assessments or participant compliance (Note: Within 3 months prior to enrollment, average weekly alcohol consumption exceeding 21 units for males or 14 units for females, where 1 unit = 360 mL of beer, 45 mL of spirits containing 40% alcohol, or 150 mL of wine. Drug abuse refers to the repeated and excessive use of drugs with dependence-producing properties or dependence potential, unrelated to recognized medical needs and for non-medical purposes);
• Individual who is currently participating in other clinical studies, or plan to participate in other clinical studies before the end of this clinical study;
• Other conditions that may impact the participant's safety or influence the assessment of vaccine response, as determined by the investigator.