Timing of Protective Immunity After Hepatitis B Vaccination
Test for protective anti-HBs antibodies 1–2 months after the final (third) dose of the hepatitis B vaccine series; this is when peak antibody response occurs and immunity can be reliably documented. 1
Standard Testing Timeline
The CDC and ACIP mandate that anti-HBs testing occur 1–2 months after completing the three-dose series (administered at 0,1, and 6 months). 1, 2, 3
Testing earlier than 1 month may underestimate the immune response because peak antibody levels have not yet developed. 3
Testing later than 2 months is acceptable but unnecessary for documentation purposes, as antibody levels naturally decline over time without indicating loss of protection. 1, 3
Use a quantitative assay (such as ELISA) capable of detecting the protective threshold of ≥10 mIU/mL; qualitative tests are inadequate. 2, 3
Antibody Response Kinetics by Dose
After the first dose, only 30–55% of healthy adults under age 40 achieve protective anti-HBs levels (≥10 mIU/mL). 1
After the second dose, approximately 75% of healthy adults reach protective levels. 1
After the third dose, >90% of healthy adults under age 40 and approximately 95% of healthy infants achieve protective immunity when tested 1–2 months later. 1, 4
The third dose functions as a true booster, producing the highest and most durable antibody titers. 1, 5
Age-Related Differences in Response
Adults over age 40 have lower seroprotection rates (<90%) and lower geometric mean titers (GMT ~610 mIU/mL) compared to younger adults. 1, 4
By age 60, only approximately 75% of vaccinated persons develop protective antibody levels. 1
Infants and children under age 10 achieve seroprotection rates of 98–99% when tested 1–2 months after the third dose. 4
Special Timing Considerations
If hepatitis B immune globulin (HBIG) was administered concurrently with vaccine (e.g., post-exposure prophylaxis), delay anti-HBs testing until 4–6 months after HBIG administration, as passively acquired antibodies interfere with accurate assessment of vaccine-induced immunity. 3
For healthcare workers and other high-risk populations, the 1–2 month testing window is mandatory to document immune status for occupational safety and guide post-exposure management. 1, 2, 6
Hemodialysis patients require testing 1–2 months after the fourth dose (given at month 6 on a 0,1,2,6 schedule) because they receive a high-dose regimen (40 µg). 1, 4
Interpretation of Results
Anti-HBs ≥10 mIU/mL indicates protective immunity; immunocompetent individuals require no further testing or booster doses. 1, 2
Anti-HBs <10 mIU/mL defines a non-responder who remains susceptible and requires revaccination. 1, 2
For non-responders, administer one additional vaccine dose immediately and retest 1–2 months later; if still <10 mIU/mL, complete a full second three-dose series. 1, 2
Duration of Protection After Seroconversion
Immunocompetent persons who achieve anti-HBs ≥10 mIU/mL after the primary series maintain protection for ≥22–30 years, even as circulating antibody levels decline below 10 mIU/mL. 1, 6
Protection persists through cellular immune memory; most vaccine responders (88%) demonstrate an anamnestic response to a challenge dose 30 years after vaccination. 1, 6
Approximately 16% of persons vaccinated as infants retain anti-HBs ≥10 mIU/mL at 18 years, compared to 74% of those vaccinated at age ≥1 year, but both groups remain protected. 1
Common Pitfalls to Avoid
Never test before 4 weeks post-final dose, as this will miss the peak antibody response and underestimate immunity. 3
Never forget that HBIG administration requires a 4–6 month delay before testing, or results will be falsely elevated from passive antibody. 3
Never use qualitative anti-HBs tests; only quantitative assays can confirm the ≥10 mIU/mL protective threshold. 2, 3
Never assume that declining antibody titers below 10 mIU/mL indicate loss of protection in immunocompetent vaccine responders; cellular immunity persists. 1, 2, 6
Never delay testing beyond 2 months unnecessarily, as this postpones clinical decision-making for non-responders who need revaccination. 3