This study will evaluate the efficacy of the Recombinant RSV vaccine(CHO cell) vaccine in preventing lower respiratory tract diseases(LRTD) caused by RSV in adults≥ 60 years of following a single dose of the RSV vaccine(CHO cell) vaccine .This study will also assess if the vaccine is safe and induces an immune response.

A total of 25000 adults aged 60 years and above will be enrolled, stratified into 60-69 and ≥70 years of age. All Participants will randomly receive investigational vaccine or placebo at a ratio of 1:1. Efficacy and safety will be assessed in all Participants, while immunogenicity will be assessed in a subset of 1200 Participants in a selected trial site.

Inclusion Criteria:

1. A male or female can provide legal identification at the time of enrollment, and is 60 years of age or older (women are required to be infertile).

   (Note: Women with infertility include those who have been menopausal or have undergone sterilization (including hysterectomy, bilateral salpingectomy, bilateral oophorectomy, etc.)

2. Be able to understand the trial procedures, risks and benefits and voluntarily agree to participate in the study and sign an informed consent.

3. Be able to participate in all scheduled visits and comply with the protocol requirements

4. Participants with stable health conditions considered by the investigator. Stable health conditions refer to patients with chronic diseases whose conditions are stable (regardless of whether they have received specific treatment or not), such as diabetes, hypertension, chronic obstructive pulmonary disease, asthma, etc. If the researcher determines that the condition is stable, they may be allowed to participate in this trial.

Exclusion Criteria:

Participants who meet any of the following exclusion criteria will not be allowed to enter the study (if the number of participants is not yet met, if the criteria described in "*" are met during screening, repeated screening may be performed)

1. *Axillary temperature>37.3℃.
2. History of RSV infection within 6 months before enrollment.
3. *New onsets of respiratory tract infection symptoms like cough, sputum, shortness of breath, wheezing, fever, runny nose or nasal congestion within 7 days before enrollment.
4. *Acute diseases or acute exacerbation of chronic disease within 3 days before vaccination.
5. *Within 3 days before enrollment, antipyretic and analgesic drugs (except enteric-coated aspirin tablets for the prevention of cardiovascular and cerebrovascular diseases) and antihistamines were used
6. Those who are allergic to the known components in the test vaccine [saponin (QS-21), dioleoyl phosphatidylcholine (DOPC), cholesterol, sucrose, sodium dihydrogen phosphate, anhydrous sodium dihydrogen phosphate, polysorbate 80, sodium chloride, hydrochloric acid and sodium hydroxide] Those who have a history of severe allergies after any vaccination or medication use [such as anaphylactic shock, allergic laryngeal edema, allergic purpura, thrombocytopenic purpura, local allergic necrosis reaction (Arthus reaction), severe urticaria, etc.] or serious adverse reactions.
7. Asplenia or functional asplenia, and any condition leading to asplenia or splenectomy.
8. Those who have had or are currently suffering from malignant tumors (except for clinically cured carcinoma in situ and papillary thyroid carcinoma).
9. Patients are diagnosed with autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease and autoimmune thyroid disease.
10. Persons with known or suspected immunodeficiency disorders [e.g. primary or secondary immunodeficiency, or diagnosed with congenital or acquired immunodeficiency, human immunodeficiency virus infection or immunosuppressive/cytotoxic agent therapy (e.g. cancer chemotherapy, organ transplantation or autoimmune disease treatment) resulting in confirmed or suspected immunosuppression or immunodeficiency].
11. According to the investigator's assessment,there is any disease that may make intramuscular injections unsafe, such as a history of thrombocytopenia or other coagulation disorders.
12. Those who have a history or are currently suffering from severe clinical diseases that have not been cured (such as severe cardiovascular and cerebrovascular diseases, liver and kidney diseases, respiratory system diseases, diabetes with complications, major surgeries, etc.) and may affect the evaluation of the trial.
13. Those who have had or are currently suffering from thrombotic diseases.
14. Patients with a history of untreated TB or active TB at enrollment.
15. *Hypertension with poor medication control (on-site blood pressure measurement before vaccination: systolic blood pressure≥150mmHg and/or diastolic blood pressure≥100mmHg).
16. Those with severe arrhythmias (such as atrial fibrillation).
17. Those with a history or family history of convulsions, epilepsy, congenital brain hypoplasia, mental illness, etc., or a history of brain nerve tissue damage caused by other serious neurological diseases (such as brain tumors, cerebral hemorrhage, brain infections, chemical drug poisoning, etc.).
18. Use of any experimental or unapproved product (drug, vaccine or medical device) other than the vaccine used in this trial or participate in other clinical trials within 30 days prior to enrollment or during the trial period.
19. *Within 14 days prior to enrollment, any non-live vaccine has been administered, or within 28 days, a live vaccine or nucleic acid vaccine has been administered.
20. Has received the RSV vaccine before.
21. Use of immunoglobulin and/or any blood preparation or plasma derivative, such as gamma globulin or intravenous human immunoglobulin, within 3 months prior to enrollment or plan to use during the trial
22. Within the 3 months prior to enrollment or if it is expected to be used for a long period during the trial (continuous for more than 14 days), immunosuppressive agents or other immunomodulatory drugs (such as long-term use of systemic glucocorticoids for ≥ 14 days, with a dose of ≥ 20mg/day prednisone or equivalent prednisone dose; local medications are allowed, such as ointments, eye drops, inhalants or nasal sprays, but the local medication dosage must not exceed the recommended dosage in the instructions)
23. Long-acting immunomodulatory drugs (such as infliximab) were used within 6 months before enrollment or during the planned trial period.
24. The researchers determined that the drinking behavior and/or drug abuse history that might affect the assessment of the trial (Note: within the last three months, men had an average of more than 14 standard drinks per week, and women had an average of more than 7 standard drinks per week; 1 standard drink contained 14g of alcohol, such as 360mL of beer or 45mL of 40% alcohol spirit or 150ml of wine.) Drug abuse refers to the repeated and excessive use of drugs with dependent characteristics or potential for dependence, which is not related to recognized medical needs and falls under non-medical purpose drug use.
25. Planned move to a location that will prohibit participating in the trial until study end;
26. Any condition that, in the opinion of the investigator, may affect the safety of the participant or the evaluation of the study results.