Once infected by single or multiple variants of HIV, the virus replicates itself into even more genetic variants, making it difficult to develop a vaccine.

• 一旦感染上艾滋病病毒，不管是单一变异体还是多种变异体的，该病毒都会自我复制成更多的基因变异体，从而给培育疫苗带来困难。