No effective vaccine against HIV has yet been produced mainly because
- A. the virus is too large for the immune system
- B. HIV infects only animals
- C. antibodies can never form against HIV
- D. the virus mutates its envelope proteins very rapidly
Explanation
The envelope glycoproteins change faster than a vaccine can be designed, and the virus hides inside cells as a provirus. Antibodies do form in infection, but they keep chasing a moving target, which is the real obstacle.
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