The recombinant hepatitis B vaccine (Engerix-B) is an example of which vaccine type, and why does it not cause hepatitis B infection?

• A Live attenuated vaccine; it is attenuated to non-pathogenic levels
• B Inactivated whole-virus vaccine; killed virus cannot replicate
• C Virus-like particle vaccine containing intact HBV without polymerase gene
• D Subunit vaccine containing only HBsAg protein produced in yeast; no viral genome present ✓

Explanation

Recombinant hepatitis B vaccine contains only the hepatitis B surface antigen (HBsAg) protein, which is produced by Saccharomyces cerevisiae yeast transformed with the HBsAg gene. Since only the surface protein is present (no HBV DNA, no core, no polymerase), it is a protein subunit vaccine and cannot cause hepatitis B infection. The self-assembling HBsAg particles form virus-like structures that are highly immunogenic but non-infectious. This was the first recombinant subunit vaccine approved for human use (1986).

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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