Which statement correctly describes the relationship between HBV and HDV infections?

• A. HDV infection can occur without HBV.
• B. HDV infection requires HBV co-infection for replication.
• C. HDV infection is independent of HBV infection.
• D. HDV infection is prevented by HBV vaccination only if HBV is fully cleared.

Answer: (B)

HDV cannot complete its life cycle without the surface antigen provided by HBV. It is a defective satellite-like virus that uses HBV’s HBsAg to envelope its own particles, so HDV replication and infectious spread depend on the presence of HBV. That’s why the statement stating that HDV infection requires HBV co-infection for replication is the best description: both co-infection (simultaneous HBV and HDV) and superinfection (HDV infecting someone already chronically HBV-positive) rely on HBV being present to supply HBsAg.

HBV vaccination blocks HBV infection, which removes the necessary component for HDV to assemble and spread, thereby preventing HDV infection. The other ideas—HDV occurring without HBV, or HDV being independent of HBV, or the notion that prevention depends on clearing HBV after infection—do not fit the biology of how HDV propagates.