Hepatitis B (HBV) is a virus that affects the liver. Not everyone with HBV will have symptoms when they are infected. HBV will usually go away on its own within 6 months, but sometimes it becomes a long-term (chronic) infection. The DNA of the virus can stay in the body even after the initial infection goes away, and infection may be reactivated under certain conditions. Drugs that weaken the immune system may increase an individual’s risk for HBV reactivation, which can cause life-threatening liver problems.