Why does vaccination against hepatitis B virus (HBV) also prevent hepatitis D virus (HDV) infections?

• A. An immunogen from HBV in the vaccine is also associated with HDV.
• B. The HBV vaccine induces formation of heterophile antibodies that cross-react with HDV.
• C. The HBV vaccine stimulates liver cells to produce antiviral molecules active against all hepatitis viruses.
• D. HDV requires the host to be concurrently infected with HBV.

Answer: (D)

The key idea is that hepatitis D virus (HDV) is a defective satellite virus that needs the hepatitis B virus (HBV) to provide its outer envelope, specifically the HBV surface antigen (HBsAg), in order to infect liver cells and assemble new particles. When you vaccinate against HBV, your immune system makes antibodies against HBsAg and prevents HBV infection and the production of HBsAg. Without HBsAg being present, HDV cannot acquire its envelope or propagate, so HDV infection cannot occur. The other statements aren’t correct because the HBV vaccine doesn’t rely on cross-reactive or non-specific antiviral effects and isn’t providing an HBV-derived immunogen that protects against HDV through other mechanisms. HDV requires concurrent HBV infection to exist, so blocking HBV with vaccination blocks HDV as well.