Which marker indicates immunity to a hepatitis B infection?

The presence of Anti-HBs, which are antibodies against the hepatitis B surface antigen (HBsAg), indicates immunity to a hepatitis B infection. This immunity can arise either from a past infection that has resolved, allowing the body to produce these antibodies, or from successful vaccination against hepatitis B. When Anti-HBs are detected in a person's serum, it signifies not only that the person has developed a protective immune response, but also that there is no active infection at that moment.

In contrast, other options provide different information about hepatitis B status. For example, Anti-HBc (IgM) is an indicator of a recent or acute infection, while HBsAg signifies active hepatitis B virus infection. Anti-HBc (IgG) indicates past infection but does not confirm immunity, as the individual may not have developed sufficient protective antibodies. Thus, the presence of Anti-HBs is specifically what confirms that an individual is immune to hepatitis B.