So far, none has proven to be effective in humans. The problem is that the AIDS virus is very complicated. It can even change once it is inside the human body. Scientists are searching for a vaccine that will work against all the different strains.
Doctors usually give immunizations against diseases such as measles to prevent infection.
In addition to looking for this type of preventive AIDS vaccine, scientists are trying to develop a new type. This would be an AIDS vaccine that will help people already infected with the AIDS virus from getting sicker. Experimental preventive and therapeutic AIDS vaccines are being tested in chimpanzees and monkeys, and in humans.