Anti-HBsAb Level Indicating Immunity Against Hepatitis B
An anti-HBs (hepatitis B surface antibody) level of ≥10 mIU/mL indicates immunity against hepatitis B virus infection. 1, 2, 3
The Protective Threshold
The CDC Advisory Committee on Immunization Practices establishes ≥10 mIU/mL as the protective concentration that defines immunity following hepatitis B vaccination. 1
This threshold must be measured using a quantitative method (such as ELISA) that can accurately detect this protective concentration. 1
Testing should be performed 1-2 months after administration of the final vaccine dose to properly assess immune response. 1
Long-Term Protection in Immunocompetent Individuals
Once an immunocompetent person achieves anti-HBs ≥10 mIU/mL after completing the primary vaccine series, they are considered to have long-term protection and do not need further periodic testing or booster doses. 1, 2, 3
This protection persists through immunologic memory even if antibody levels subsequently decline below 10 mIU/mL, as the immune system retains the ability to mount a rapid anamnestic response upon exposure. 4
Studies demonstrate that protective immunity can persist for over 10 years following vaccination, regardless of whether booster doses are administered. 5
Special Populations Requiring Different Management
Immunocompromised Patients
Annual testing to assess anti-HBs concentrations is recommended for immunocompromised persons (including HIV-infected individuals, hematopoietic stem-cell transplant recipients, and those receiving chemotherapy). 1, 3
Revaccination should be considered when anti-HBs falls below 10 mIU/mL in these patients. 3
Hemodialysis Patients
- Annual monitoring of anti-HBs levels is recommended, with booster doses administered if levels fall below 10 mIU/mL. 3
Healthcare Personnel
- Pre-exposure assessment of anti-HBs upon hire or matriculation is recommended to ensure protection in case of occupational exposure. 1
Management of Inadequate Response
If anti-HBs is <10 mIU/mL after the primary vaccine series, revaccination with a complete second series is indicated, followed by retesting 1-2 months after the final dose. 1, 3
If anti-HBs remains <10 mIU/mL after two complete vaccine series, testing for HBsAg should be performed to rule out chronic hepatitis B infection. 1, 3
Persons who fail to respond to two complete vaccine series should be considered susceptible and counseled about precautions to prevent HBV infection, including the need for HBIG prophylaxis after known exposures. 1
Important Caveats
The ≥10 mIU/mL threshold as a correlate of vaccine-induced protection has only been validated for persons who have completed an approved vaccination series. 1, 3
Testing unvaccinated or incompletely vaccinated individuals for anti-HBs is potentially misleading and should not be used to determine immunity. 1, 3
Different assays may have different cutoff values, so clinicians should refer to the package insert of the specific test being used. 1