Which vaccine type is defined by using specific antigens, such as the hepatitis B surface antigen?

• A. Live Attenuated Vaccines; Example MMR
• B. Inactivated Vaccines; Example Influenza Shot
• C. Subunit Vaccines; Example Hepatitis B Surface Antigen
• D. Toxoid Vaccines; Example Tetanus Toxoid

Answer: (C)

Subunit vaccines rely on specific antigens from a pathogen rather than the whole organism. The hepatitis B vaccine uses the hepatitis B surface antigen as the immunizing component. This protein is produced separately (often via recombinant technology) and purified to stimulate antibodies against the virus without introducing infectious particles. Because only the defined antigen is presented, the approach tends to have a favorable safety profile, though some formulations may require adjuvants or multiple doses to achieve strong immunity.

Other vaccine types involve broader components: live attenuated vaccines use a weakened whole microbe that can replicate, inactivated vaccines use a whole killed microbe, and toxoid vaccines use inactivated toxins. These strategies expose the immune system to larger or different parts of the pathogen, rather than a single defined antigen.