Hepatitis D
Hepatitis D (HDV) is a defective RNA virus which cannot survive on its own.
This blood-borne pathogen only infects liver cells which are co-infected with Hepatitis B virus.
There is no vaccine against this strain of hepatitis.
Neither interferon nor transplantation is effective in the fight against hepatitis D.
On the bright side, if you are immune to HBV, you will also be immune to HDV.