Hepatitis B is a serious liver infection caused by the hepatitis B virus (HBV) that can lead to acute or chronic illness. Chronic hepatitis B can increase the risk of severe liver damage, including cirrhosis and liver cancer. Fortunately, a safe and effective vaccine exists to prevent this infection. Many wonder if contracting Hepatitis B is possible even after vaccination, making it important to understand the vaccine’s protection and rare infection scenarios.
Hepatitis B Vaccine Efficacy and Protection
The Hepatitis B vaccine is highly effective in preventing infection. After completing the recommended series of three doses, the vaccine provides robust protection. This immunization prompts the immune system to produce specific antibodies (anti-HBs) that recognize and neutralize the virus if a vaccinated person is exposed.
For most healthy adults, the vaccine achieves a seroprotection rate of 90-95%, while in infants and children, this rate can be as high as 98-100%. The protection conferred by the vaccine is generally long-lasting, often extending for over two decades, and immune memory can persist for 30 years or more. Even if antibody levels decrease over time, the immune system often retains a memory that allows for a rapid protective response upon exposure. This enduring immune memory helps to prevent clinical disease, even if antibody levels fall below detectable protective thresholds.
Scenarios for Hepatitis B Infection After Vaccination
While the Hepatitis B vaccine offers strong protection, specific, albeit rare, circumstances allow a vaccinated individual to still be susceptible. One scenario involves individuals who do not develop a sufficient immune response after vaccination, known as non-responders. Approximately 5-15% of vaccinated individuals may not produce adequate protective antibodies after completing the full vaccine series.
Factors contributing to non-response include older age, obesity, smoking, and certain chronic health conditions such as diabetes, kidney disease, liver disease, HIV, celiac disease, or inflammatory bowel disease. Genetic predispositions also influence an individual’s ability to mount a protective antibody response. An anti-HBs level less than 10 mIU/mL is generally considered non-protective.
Waning immunity over time is another consideration. While protection is typically long-term, antibody levels can gradually decline in some individuals many years after vaccination. Despite this decrease, the immune system’s memory often provides continued protection against serious infection. Breakthrough infections in vaccinated individuals are uncommon and, when they occur, are often transient, meaning the body successfully clears the virus without developing chronic disease.
Infection could also occur if an individual is exposed to the virus before developing full immunity. The complete vaccine series (typically three doses) and sufficient time for the immune response to build are necessary for optimal protection. Exposure to HBV during this window, or between doses, could lead to infection. The theoretical possibility of vaccine-escape mutants exists, but this is exceedingly rare for Hepatitis B and not a primary concern for most people.
Confirming Your Immunity and Taking Action
For individuals concerned about their immunity after Hepatitis B vaccination, a simple blood test can provide clarity. This HBsAb or anti-HBs test measures the level of protective antibodies in the blood. A result of 10 mIU/mL or greater is generally considered protective, indicating sufficient antibodies to resist infection. Conversely, a result below this threshold suggests a lack of protective immunity.
If test results indicate a non-protective antibody level, consulting a healthcare professional is advisable. Options may include re-vaccination, sometimes using a different vaccine brand or an increased dose. A second full series can lead to a protective response in 30-50% of previous non-responders. Booster shots may also be recommended for individuals with waning immunity, particularly for those who are immunocompromised or at continued high risk of exposure. In cases of known exposure to the virus for non-responders, Hepatitis B immunoglobulin (HBIG) might be administered to provide immediate, temporary protection.