A healthcare worker completed the hepatitis B vaccine series. Post-vaccination testing shows an anti-HBs titre of less than 10 mIU/mL. What does this indicate and what is the appropriate action?

Correct answer: A. Non-response — revaccination with a further series is indicated

• A. CORRECT. An anti-HBs titre BELOW 10 mIU/mL measured 1–2 months after completing the series defines a NON-RESPONDER. The recommended action is a second complete three-dose series followed by repeat testing. Those who remain negative after two full series are considered permanently susceptible and must be managed with hepatitis B immune globulin after any percutaneous exposure to an HBsAg-positive source.
• B. Anti-HBs is the ANTIBODY to surface antigen and is a marker of immunity, not of infection. Active infection is indicated by HBsAg (surface ANTIGEN) positivity, not by a low antibody titre.
• C. Prior natural infection produces anti-HBc (core antibody) in addition to anti-HBs. A low anti-HBs with no core antibody indicates failure to respond to vaccine, not past infection.
• D. A titre of 10 mIU/mL OR ABOVE indicates adequate immunity. Below that threshold the response is inadequate, so no action would be unsafe.

Note: Reading the hepatitis B serology panel: HBsAg positive means current infection. Anti-HBs positive alone means immunity from VACCINATION. Anti-HBs plus anti-HBc positive means immunity from RESOLVED NATURAL INFECTION. Anti-HBc alone can indicate the window period or a resolved infection with waning antibody. Non-response is more common with increasing age, obesity, smoking and immunosuppression.