After completing the Hepatitis B vaccine series, which blood result demonstrates immunity?

• A. Positive anti-HBs
• B. Positive IgG
• C. Positive HBsAg
• D. Positive IgM

Answer: (A)

Immunity after hepatitis B vaccination is shown by the presence of antibodies to the hepatitis B surface antigen (anti-HBs). The vaccine teaches the immune system to recognize HBsAg, so a protective anti-HBs titer develops. When anti-HBs is detected, it means you’ve produced the specific antibodies needed to neutralize the virus and you’re considered protected, typically with a protective level around 10 mIU/mL or higher.

Why this fits: the vaccine contains the surface antigen, so the immune response targets that antigen and yields anti-HBs. Other serology markers aren’t indicators of vaccine-induced immunity. HBsAg positivity means the virus is present and infection is ongoing. IgM indicates acute infection. A generic IgG result isn’t specific enough to prove immunity after vaccination, since anti-HBs is the specific antibody produced in response to the vaccine, and anti-HBc antibodies would indicate past or current infection rather than vaccine-induced immunity.