If an employee vaccinated against hepatitis B is exposed to the virus and the employee's vaccine response is unknown, what post-exposure follow-up step should be performed first?

• A. Perform baseline testing for HBV antibodies.
• B. Administer HBV immune globulin immediately.
• C. Repeat vaccination series immediately.
• D. Wait for seroconversion before taking any action.

Answer: (A)

Baseline testing for hepatitis B surface antibodies should be performed first after exposure in a vaccinated employee with unknown vaccine response. This test shows whether the person has protective anti-HBs antibodies (typically a titer ≥10 mIU/mL). If the anti-HBs is protective, no further post-exposure prophylaxis is needed for HBV. If it isn’t protective, you then initiate the appropriate measures (HBIG within 7 days of exposure and restarting or completing the vaccination series). Waiting for seroconversion would delay protection, and giving immune globulin or repeating the vaccine series without knowing the antibody status isn’t as effective or targeted. Checking the baseline antibody level first guides the subsequent, evidence-based steps.