Hepatitis B is a viral infection that targets and inflames the liver. The Hepatitis B Virus (HBV) can cause both acute illness and chronic infection, potentially leading to severe complications like cirrhosis or liver cancer. Immunity against HBV means the immune system can recognize and neutralize the virus, preventing it from establishing an infection. Protection from future infection is definitively possible.
Pathways to Hepatitis B Immunity
Immunity to the Hepatitis B virus is established through vaccination or natural recovery from a past infection. Both pathways generate specific protective antibodies that circulate in the bloodstream. These antibodies recognize the virus’s surface proteins, known as the Hepatitis B Surface Antigen (HBsAg), and block the virus from entering liver cells.
The most reliable path to immunity is the Hepatitis B vaccine. The vaccine introduces a non-infectious, engineered version of the HBsAg protein to safely stimulate the immune system. A complete vaccination series typically involves two to three doses administered over several months to ensure a lasting immune response.
Immunity also results from the successful natural clearance of an acute HBV infection. If the body clears the virus entirely, the infection resolves, and the immune system retains a memory of the virus. This memory is maintained by protective antibodies that remain in the blood after the HBsAg has disappeared.
This natural immunity only occurs after the resolution of an acute infection. Individuals with a chronic infection, where the virus persists for more than six months, are not considered immune because their body failed to eliminate the virus.
Confirming Immunity Through Serology
Immunity to Hepatitis B is confirmed through a serology panel, a blood test that measures specific viral components and corresponding antibodies. This panel examines three main markers: the Hepatitis B Surface Antigen (HBsAg), the Hepatitis B Surface Antibody (Anti-HBs), and the Hepatitis B Core Antibody (Anti-HBc). Immunity interpretation relies on the combination of positive and negative results for these markers.
The presence of HBsAg indicates an active infection, meaning the virus is currently present and the person is infectious. For a person to be considered immune, this marker must be negative. The Anti-HBs is the marker for protection; its presence confirms the body has developed neutralizing antibodies. A positive Anti-HBs result, defined as 10 mIU/mL or greater, confirms immunity from either vaccination or resolved natural infection.
The Anti-HBc is a sign of past or current exposure to the whole virus. Since the core antibody responds to the internal part of the virus, which is not in the vaccine, it helps differentiate the source of immunity. A positive Anti-HBs combined with a negative Anti-HBc indicates immunity from vaccination. A positive result for both Anti-HBs and Anti-HBc indicates immunity from a successfully cleared natural infection.
Long-Term Status of Hepatitis B Immunity
Once confirmed by a positive Anti-HBs test, protection against the Hepatitis B virus is generally considered long-term, often lasting a lifetime. The immune system maintains memory cells that quickly produce new antibodies if the virus is encountered again. This immune memory provides continuous protection, even if measured antibody levels in the blood decrease over time.
Routine booster doses are not recommended for individuals with normal immune function who completed the vaccine series. Even if later testing shows the Anti-HBs level has dropped below the protective threshold of 10 mIU/mL, the immune memory is usually sufficient to prevent infection. Exceptions include immunocompromised populations or those with specific medical conditions, such as kidney dialysis patients, who may require periodic antibody testing and booster shots.
In rare cases, typically in individuals with severe immunosuppression, established immunity may be compromised. This increases the risk of HBV reactivation, which is the resurgence of a previously controlled infection. This risk is higher for those whose immunity was established through natural clearance and who still have a positive Anti-HBc marker. For the majority of healthy people, confirmed immunity is a durable defense against HBV.