The purpose of this observational study is to follow up on chronic HBV-infected patients over a long period of time to understand the changes in the immune status as age increases and the natural history of chronic HBV infection progresses. The main questions it aims to answer are: * Does the natural history of chronic HBV infection progress with changes in HBV-specific immunity? * What is the role of age in the natural history of chronic HBV infection? Patients with chronic HBV infection who are untreated and aged 1-80 years will be followed up every six months. During each follow-up, HBV-related serological and virological indicators will be tested. Peripheral blood samples will also be collected to test HBV-specific immunity and the immune environment.