HIV is hard to immunize against because it targets immune cells. Some types of immune cells that bear HIV-binding antibodies may actually vacuum up viruses and

HIV is hard to immunize against because it targets immune cells. Some types of immune cells that bear HIV-binding antibodies may actually vacuum up viruses and infect themselves. Some vaccines have increased the likelihood of pervasive HIV infection. The trick will be to make a vaccine that only stimulates the production of HIV-non-susceptible cells. Hepatitis B mutates about as rapidly as HIV. Although it is a DNA virus, it replicates from the RNA stage using a sloppy, unreliable reverse transcriptase. (Wikipedia quotes a mutation rate of >1 per nucleotide per year.) But hepatitis B does nothing special to immune cells, so when they vacuum up a virus particle it dies.