Why is it so difficult to get a vaccine for aids?

i know they say it is difficult but ihave no clue or idea why?

There are many reasons why an AIDS vaccine is difficult to develop. Here is an admittedly incomplete list:

1. HIV is highly mutable - it can change its genomic RNA sequence (altering its protein sequence) and the ability of our body to recognize the infection. As such, knowing which sequence to choose for a vaccine is very difficult.

2. The virus has evolved to adapt to localized populations, resulting in numerous "clades" found world-wide. Therefore, it may be impossible to generate one vaccine that will target all clades and multiple clade-specific vaccines will be required.

3. Scientists do not understand how most vaccines work, particularly those against viral infections. The vaccines in use today were mainly identified based on trial and error and mainly generate antibody responses - not T cell responses. While this single arm of the immune response seems to be protective against most bacterial infections (and some viral diseases), it does not appear to be protective against HIV. The common approaches used against other pathogens have failed. Therefore, generation of an HIV vaccine requires us to learn a lot more about vaccine design in general.

4. While there are rare people who appear to be resistant to HIV infection or can survive for many years without developing symptoms of AIDS, scientists do not yet understand what type of immune response is protective against HIV. Therefore, there is no "gold standard" for a vaccine to try to mimic.

5. There is no small animal model of HIV infection. The closest model system for testing potential HIV vaccines is to use monkeys. This is difficult (scientifically and ethically), time-consuming, and very expensive - and there is still debate as to how well this system recapitulates human disease. Therefore, the process is very slow from conception to testing of a new vaccine candidate.

6. Along this line, current medical ethics (as well as cost, etc.) prevent doctors from testing unproven vaccine candidates directly on humans, as might have occured 100 years ago, for fear of unanticipated side effects ("do no harm"). Before any vaccine is tested in people, it must pass numerous preliminary stages using animals and small-scale (Phase I) trials in humans before any test of vaccine efficacy (requiring a large population) is begun.

Don't loose hope - there are several good HIV vaccine candidates in the pipeline and pharmaceutical companies (i.e. Aventis Pasteur, Merck) are begining to team up to combine their approaches with some recent success.

Vaccines work by introducing your body to weakened or dead forms of the virus. By being exposed to these weakened viruses, your immune system "learns" how to recognize and destroy that virus.

Some viruses mutate (change their DNA structure) very rapidly. It's very difficult to develop vaccines for these types of viruses. By the time researchers have isolated a vaccine and distributed it to people, the virus has changed. Because the "new" virus has a different DNA code than the virus contained in the vaccine, the immune system does not recognize it as the same virus. This is why influenza vaccine changes every year, because the strains of virus that it vaccinates against also change.

The HIV virus, which causes AIDS, mutates very rapidly. That's why it's so difficult to develop an effective vaccine

The quick answer is this: The virus mutates at such a high rate that it makes the creation of a vaccine very difficult. Vaccines will only work on the specific mutation it is desgined for, or ones close thereto.