How is adequate immunity to Hepatitis B (HB) vaccine measured?

Measuring Adequate Immunity to Hepatitis B Vaccine

Adequate immunity to Hepatitis B vaccine is measured by testing anti-HBs levels 1–2 months after the final vaccine dose using a quantitative method (such as ELISA), with a protective threshold of ≥10 mIU/mL. 1

Testing Method and Timing

• Use a quantitative assay (e.g., enzyme-linked immunosorbent assay [ELISA]) that can detect the protective concentration of anti-HBs ≥10 mIU/mL. 1
• Test 1–2 months after the last dose of the vaccine series to accurately assess peak antibody response. 1
• Testing earlier than 1 month may underestimate the immune response, while testing later is unnecessary for documentation purposes. 2

Interpretation of Results

Adequate Response (Anti-HBs ≥10 mIU/mL)

• Persons with anti-HBs ≥10 mIU/mL are considered immune and protected against HBV infection. 1
• Immunocompetent individuals have long-term protection and do not need further periodic testing to assess anti-HBs levels. 1
• No booster doses are currently recommended for immunocompetent persons who achieve this threshold. 3, 4

Inadequate Response (Anti-HBs <10 mIU/mL)

• Revaccinate with a complete second vaccine series on an appropriate schedule. 1
• Retest anti-HBs 1–2 months after the final dose of the second series. 1
• If still <10 mIU/mL after two complete series, test for HBsAg to rule out chronic HBV infection. 1

Who Should Be Tested Post-Vaccination

The CDC recommends post-vaccination serologic testing for specific high-risk populations: 1

• Healthcare personnel and public safety workers at risk for blood or body fluid exposure
• Hemodialysis patients and those who might require outpatient hemodialysis
• HIV-infected persons and other immunocompromised persons (e.g., hematopoietic stem-cell transplant recipients, persons receiving chemotherapy)
• Sex partners of HBsAg-positive persons
• Infants born to HBsAg-positive mothers

Special Populations Requiring Modified Management

Immunocompromised Patients

• Annual testing of anti-HBs concentrations may be warranted to assess ongoing immunity. 1, 3
• Revaccinate when anti-HBs falls <10 mIU/mL. 3

Hemodialysis Patients

• Require higher vaccine doses (40 μg) compared to standard dosing. 3
• Need annual monitoring with booster doses if anti-HBs <10 mIU/mL. 3

Healthcare Personnel Who Received HBIG

• Wait 4–6 months after HBIG administration before testing anti-HBs levels, as passively acquired antibodies from HBIG interfere with accurate assessment of vaccine-induced immunity. 1, 2
• Testing must occur after anti-HBs from HBIG is no longer detectable (approximately 6 months). 1

Critical Pitfalls to Avoid

• Do not test unvaccinated or incompletely vaccinated persons for anti-HBs, as the ≥10 mIU/mL correlate of vaccine-induced protection has only been validated for those who completed an approved vaccination series. 1, 3
• Do not use qualitative tests—only quantitative assays can confirm the protective threshold of ≥10 mIU/mL. 1, 2
• Do not test earlier than 1 month post-vaccination, as this may underestimate peak antibody response. 2
• Do not forget HBIG interference—testing too early after HBIG administration can yield falsely elevated results that don't reflect vaccine response. 2

Additional Serologic Testing Considerations

• Prevaccination testing (anti-HBc, HBsAg, and anti-HBs) should be performed for certain high-risk groups, including household/sexual/needle contacts of HBsAg-positive persons, HIV-positive persons, and persons born in high-endemic regions. 3
• The pattern of negative HBsAg, negative anti-HBc, positive anti-HBs definitively distinguishes vaccine-derived immunity from immunity acquired through natural infection. 4