Why the development of vaccine is difficult for AIDS?

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  • An HIV vaccine cannot consist of attenuated, actively replicating (live) HIV, due to possible reactivation.
  • Killed whole virus (like the polio vaccine) might also be dangerous because one could not be sure one has killed all viral particles. A killed whole virus vaccine had also worked poorly in animal studies.
  • There were successful vaccines that use subunits of viruses such as individual proteins: an example was the hepatitis B vaccine. However medical science was less experienced with them.
  • There isno truly useful small animal model for studying HIV infectionand vaccines had to be developed in monkeys using SIV or the artificial monkey/human virus SHIV in monkeys, which did not have exactly the same immune effects as HIV.
  • We do not know with certainty which immune response will provide protection; this is a major problem. Pre-efficacy studies of vaccines in monkeys and humans used correlates of immunogenicity such as CD8 cell response, but we do not know whether this immune response is in fact a correlate of efficacy.
  • We have never before attempted to develop a vaccine against a retrovirus like HIV. Retroviruses, by integrating their genome into ours, are able to hide completely from immune surveillance within quiescent lymphocytes. This means that any vaccine has a small window of opportunity in which to prevent infection and would have to be extremely effective, repelling all attempts by HIV to attach to and infect host cells.
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