The goal of this clinical trial is to evaluate the safety, tolerability, immunogenicity and Pharmacokinetics (PK) characteristics of SA1211 Injection in healthy volunteers (Part A) and participants with chronic hepatitis B (CHB, Part B), and assess its preliminary efficacy in participants with chronic hepatitis B (CHB). The main questions it aims to answer are:

What are the safety, tolerability, immunogenicity and PK characteristics of a single subcutaneous injection of SA1211 Injection in healthy volunteers (Part A)? What are the safety, tolerability, immunogenicity and PK characteristics of multiple subcutaneous injections of SA1211 Injection in participants with CHB (Part B)? What is the preliminary efficacy of SA1211 Injection in participants with CHB (Part B)?

Participants will:

• Part A (healthy volunteers): Receive a single subcutaneous injection of SA1211 Injection or placebo and complete relevant safety, tolerability and PK monitoring as required.
• Part B (participants with CHB): Receive multiple subcutaneous injections of SA1211 Injection or placebo and complete relevant safety, tolerability, PK monitoring and preliminary efficacy assessment as required.

Inclusion Criteria:

1. Able to correctly understand and sign the informed consent form in writing.

2. Male or female participants.

   • For healthy participants: aged 18-55 years old (inclusive of the cut-off values).
   • For participants with chronic hepatitis B (CHB): aged 18-65 years old (inclusive of the cut-off values).

3. Body Mass Index (BMI) meets the following requirements.

   • For healthy participants: within the range of 18-28 kg/m² (inclusive of the cut-off values).
   • For participants with chronic hepatitis B (CHB): within the range of 18-32 kg/m² (inclusive of the cut-off values).

4. During the screening period, the results of the following examinations are either normal or abnormal but not clinically insignificant:

   - Clinical laboratory tests: complete blood count, blood biochemistry, coagulation function, urine routine. Thyroid function test. 12-lead electrocardiogram (ECG). Abdominal ultrasound. Posteroanterior chest X-ray.

5. For participants with chronic hepatitis B (CHB): documented hepatitis B virus (HBV) infection for at least 6 months before screening, with positive hepatitis B surface antigen (HBsAg) and/or positive HBV deoxyribonucleic acid (HBV DNA).

6. For female participants of childbearing potential: must not be pregnant or lactating, and agree to use effective contraception during the study period.

7. For male participants of childbearing potential: agree to use effective contraception during the study period to ensure effective contraception for their sexual partners.

Exclusion Criteria:

1. Participants with concurrent hepatitis C virus (HCV), human immunodeficiency virus (HIV) or syphilis infection; or those previously diagnosed with hepatitis A, D, or E who have not been cured.
2. Participants with severe diseases, including but not limited to diseases of the nervous, cardiovascular, hematological and lymphatic, immune, renal, hepatic, thyroid, gastrointestinal, respiratory, metabolic, and skeletal systems, as well as a history of malignant tumors.
3. Participants with severe mental illness or uncontrolled mental disorders, including but not limited to schizophrenia, bipolar disorder, or depression.
4. Participants with a systolic blood pressure ≥140 mmHg or diastolic blood pressure ≥90 mmHg at screening, who are deemed unsuitable for the study by the investigator.
5. Participants who have undergone major surgery within 6 months before screening, or plan to undergo surgery during the study period.
6. Participants with severe infection or trauma within 4 weeks before screening.
7. Participants with a severe allergic constitution, or a confirmed allergy to this product or its formulation components.
8. Participants who smoked more than 5 cigarettes per day or the equivalent amount of tobacco within 3 months before screening.
9. Participants deemed unsuitable for the trial by the investigator due to other factors.