Observational cohort of adults with acute and chronic hepatitis B infection in Zambia, with and without HIV coinfection. Participants join the study at the time of diagnosis and before or at the time when they are starting antiviral treatments and then they are followed up over multiple years to assess changes to their liver and evolution of HBV (and HIV if applicable) infection. All treatments for HBV and HIV are standard per local Ministry of Health guidelines.

Inclusion Criteria:

Must meet the inclusion criteria for one of 5 groups, as follows:

• Group 1 (rx-naive chronic hbv mono): 18+ years old, HBsAg-positive, HIV-negative, eligible for tenofovir-based therapy, reports taking therapy no more than 7 days (could have previously taken if has stopped >1 year ago).
• Group 2 (acute hbv mono): 18+ years old, HBsAg-positive, HIV-negative, acute/subacute onset of hepatitis signs and symptoms and ALT >10 times upper limit of normal
• Group 3 (rx-naive hbv/hiv coinfection): 18+ years old, HBsAg-positive, HIV-negative, eligible for tenofovir-based therapy, reports taking therapy no more than 7 days (could have previously taken if has stopped >1 year ago).
• Group 4 (rx-experienced coinfection with hbv persistence): 18+ years old, history of chronic HBV infection based on two tests 6 months apart, HIV-positive, at least 4 years of tenofovir-based antiviral therapy, currently HBsAg-positive
• Group 5 (hbsag loss): 18+ years old, HIV-positive or negative, history of chronic HBV infection based on two tests 6 months apart, Currently HBsAg-negative confirmed by sensitive assay

Exclusion Criteria:

• Hepatitis C coinfection (antibody-positive and RNA-positive), current or recent (past 6 weeks) pregnancy, decompensated cirrhosis on physical examination, unlikely to remain in Lusaka for study duration

This study will occur in Lusaka, Zambia, which has 12% adult HIV prevalence and ~4% adult HBsAg-positivity. Both HIV and HBV treatment are free and provided through the Ministry of Health. Tenofovir-based therapies are used for HBV monoinfection and HBV/HIV coinfection. Potential participants will be recruited from Ministry of Health (i.e., public sector) clinics at study sites including from a pool of participants in past HBV research projects. There are a 5 groups of participants we seek to enroll in the study, to facilitate addressing the scientific goals of the cohort.

All study results and anonymized participant data will be made publicly-available. The timing will be based on when analysis is completed and results are disseminated. The study also will adhere to Zambian laws around data protection and sharing.

Supporting information will be made available at study completion. IPD will be made available after completion of primary outcome analyses. We expect primary outcomes analyses will be completed in 2027, 2028, and 2029.

During the study, only staff in Zambia and collaborating investigators will have access to IPD and supporting information. After the end of the study, this will be gradually made publicly available.