The study will evaluate the safety, tolerability, and immunogenicity of 2 dose levels of IN006 in healthy participants who aged at 60 years or older; of a revaccination of IN006 given 12 months or 24 months after the initial vaccination.

Inclusion Criteria:

1. Healthy participants aged ≥60 years, male or female.
2. The participants signed the informed consent form, and were able to provide valid identification documents. They also understood and complied with the requirements of the trial protocol.
3. Female participants must be non-childbearing potential. If male participants have female partners of childbearing potential, they must agree to use effective contraception from the signing of informed consent until 6 months after each vaccination.
4. Participants must be capable of performing self-care and routine activities of daily living.

Exclusion Criteria:

1. Body Mass Index (BMI) <18 kg/m^2 or ≥30 kg/m^2.

2. During the screening period, laboratory test results were abnormal and had clinical significance, or the severity reached or exceeded the Grade 2 criteria; or 12-lead electrocardiogram results were abnormal and had clinical significance (except for heart rate, for which the criterion relevant to pulse rate in exclusion criterion #3 should be applied). (For laboratory tests, a retest can be conducted at the discretion of investigators to determine the eligibility of the participants).

3. Vital signs meeting any of the following:

   • Systolic blood pressure <90 mmHg and/or diastolic blood pressure <50 mmHg;
   • Poorly controlled hypertension: systolic blood pressure ≥160 mmHg and/or diastolic blood pressure ≥100 mmHg;
   • Pulse rate >100 beats per minute or <50 beats per minute;
   • Axillary temperature >37.0°C.

4. Tattoos, scars, bruises, or other conditions at the injection site that may interfere with local reaction assessment.

5. Known allergy to the investigational vaccine or its excipients, or history of severe allergic reactions to other vaccines, foods, or medications.

6. Previously received any investigational or licensed Respiratory Syncytial Virus (RSV) vaccine, or administration of investigational/licensed RSV prophylactic monoclonal antibodies within the last 6 months.

7. Received inactivated, subunit, or recombinant influenza vaccine within 14 days prior to randomization, or any other vaccine within 28 days prior to randomization; Or plan to receive any vaccines within 28 days after the investigational vaccine.

8. Use of antipyretics, analgesics, or anti-allergic drugs within 3 days prior to randomization.

9. Have received blood or blood-related products (including immunoglobulins) within 3 months prior to randomization, or had planned to use during the trial.

10. Participants with the following diseases (based on inquiry and/or relevant diagnosis):

    • A history of acute respiratory infection within 2 weeks of randomization; Or a history of confirmed RSV-associated respiratory infection within 3 months prior to vaccination; Or during the screening, RSV IgM is positive;
    • Any acute illness or acute exacerbation of a chronic illness within 3 days prior to randomization;
    • History of congenital or acquired immune deficiency or autoimmune diseases, or long-term use (continuous use > 14 days) of corticosteroids (dose ≥ 20mg/day prednisone or equivalent dose) or other immunosuppressants within the past 6 months;
    • Participants who have been diagnosed with or currently have an infectious disease (including hepatitis B, hepatitis C, and acquired immune deficiency syndrome), those who currently have active tuberculosis, or those whose tests for hepatitis B surface antigen, hepatitis C antibody, or human immunodeficiency virus antibody are positive;
    • Previous or current neurological disorders (excluding seizures other than febrile seizures in children, and other types of epilepsy); History or family history of mental illness;
    • Asplenia, or functional asplenia;
    • Have a history of myocarditis, pericarditis or idiopathic cardiomyopathy, or have any disease that increases the risk of myocarditis or pericarditis;
    • Has a history of inflammatory demyelinating neurological disorders such as Guillain-Barré syndrome;
    • Has severe or unstable cardiovascular diseases, diabetes, diseases of the blood and lymphatic systems, immune system diseases, liver and kidney diseases, respiratory diseases, metabolic and skeletal diseases, or malignant tumors;
    • Has contraindications for intramuscular injections and blood drawing;

11. Have a history of major surgery within 3 months prior to randomization or planned surgery during the trial.

12. Drug/alcohol abuse within 1 year prior to randomization, deemed by investigators to impact safety assessment or compliance.

13. Have received lipid nanoparticle (LNP)-based vaccines/medications within 1 year prior to randomization; current participation in other RSV-related trials; OR planned to participate in other clinical trials during this study.

14. The investigators evaluated that any disease or condition of the participants might place them at an unacceptable risk; The participants failed to meet the requirements of the protocol; circumstances that interfered with the assessment of the vaccine response.