This is a multicenter, randomized, double-blind, parallel group, 48-week follow-up, Phase IIa clinical study. This study has been designed to evaluate the change in HBsAg (log10 IU/mL) after administration of hzVSF-v13 50 mg/dose and hzVSF-v13 200 mg/dose in combination with an oral antiviral agent (Tenofovir or entecavir, including salt-free or salt-modifying drugs) compared to an oral antiviral agent in combination with a placebo (normal saline) in patients with chronic hepatitis B who are stably receiving an oral antiviral agent (Tenofovir or entecavir, including salt-free or salt-modifying drugs) for at least 24 weeks.

Among the subjects who provided a voluntary written consent to participate in this clinical study, the patients with chronic hepatitis B who are stably receiving an oral antiviral agent (Tenofovir or entecavir, including salt-free or salt-modifying drugs) for at least 24 weeks prior to the screening visit can be considered as potential subjects of this study. Only the subjects who completed the final eligibility evaluation at the baseline visit (Visit 2) after the screening tests will be randomized to the hzVSF-v13 50 mg combination group, hzVSF-v13 200 mg combination group (study group) and placebo combination group (control group) at a 1:1:1 ratio at each site. The randomized subjects will receive intravenous administration of hzVSF-v13 or the placebo to match hzVSF-v13 four times with 4 weeks interval for a total of 12 weeks, and oral administration of 1 tablet of an oral antiviral agent will be given once daily for a total of 48 weeks.

Inclusion Criteria:

1. Those who have a history of a diagnosis of chronic hepatitis B more than 24 weeks prior to screening and have been maintaining HBsAg positive at screening
2. Those who have an HBV DNA level that is below <20 IU/mL
3. Those who have been receiving tenofovir (including Tenofovir's salt-free or salt-modifying drugs), or entecarvir (including Entecavir's salt-free or salt-modifying drugs) stably for ≥24 weeks prior to screening and anticipated to maintain the identical drug with equivalent dosage and administration during the clinical trial.

Exclusion Criteria:

1. Those with a history of clinically significant chronic liver disease caused by other than chronic HBV infection at the time of screening
2. Patients with a signs of loss of liver function and decompensation of liver disease
3. Patients with uncontrolled diabetes (HbA1c >7.5%)
4. Patients with uncontrolled hypertension

It will be depending on internal discussion.