To create a vaccine, scientists isolate and grow a large quantity of the virus, then find a way to destroy its DNA or RNA center without destroying all the protein coat. Then the protein coat, or parts of it, are injected into a person's body. The person's immune system reacts to the presence of the viral proteins and creates antibodies. The ability to make these antibodies remains with the person for years, or in some cases, for a lifetime. Currently, genetically engineered bacteria are also being used to create viral proteins.
If the vaccinated person ever encounters a living form of the same virus, and the virus gets into his or her bloodstream, antibody production begins immediately. In theory, the antibodies will neutralize the virus before the virus can do any harm.
Vaccines do have risks. Sometimes not all the DNA or RNA of the original virus is destroyed, and strands, once infected into the body, are able to get into a host cell and begin replication. The result: the vaccinated person gets the disease. This event is rare but it happens. Also, some people have negative reactions to the vaccine, ranging from mild conditions, like a rash, to severe ones, like shock.
Thus, vaccines are risky for the first people to try them. The potential benefit must exceed the risk. Not all vaccines are given to everybody; some vaccines, such as the recently developed hepatitis B (HBV) vaccine, are given only to certain individuals who engage in high-risk behaviors, namely, health care workers, who are often exposed to HBV-infected blood; and, to sexually active homosexual males, who are at risk of catching hepatitis B sexually.
As far as retrovirus HIV is concerned, several problems present themselves in the development of a vaccine. First, there has never been a 100% effective vaccine for a retrovirus. With our current knowledge or biology and chemistry, it is theoretically possible to create a vaccine; but remember, in biology, there are no guarantees. Everyone thinks of the Salk polio vaccine when they think of vaccines, but a repeat of this success is never guaranteed.
Second, different strains of HIV have slightly different protein coats, and thus the antibodies produced against one strain of virus may not work against another strain. Ideally, a vaccine would be based on some antigenic part of the viral protein coat that remains the same for all strains of HIV. Finally, anti-HIV antibodies seem to have no affect in HIV-infected individuals. So vaccines, even if they successfully produce antibodies, may not work.
No one truly knows when and if a vaccine for HIV will be successfully developed. It would not be wise, at this time, to rely upon the development of a vaccine to solve the AIDS problem. A vaccine will not help anyone who has already been exposed to HIV, so everyone must protect themselves against exposure.