United Nations AIDS chief predicts a vaginal gel that protects women from contracting HIV during intercourse could be ready in as little three to four years. According to UNAIDS chief, Peter Piot, a gel designed to prevent transmission of the HIV virus during sex is the best development next to an actual AIDS vaccine - which is nowhere near discovery. The microbicide would come in the form of a gel or an ovule that's put in the vagina before intercourse and immediately kills the virus upon contact. Piot compared it to a contraceptive spermicide. Researchers have been working on an AIDS vaccine for over 20 years. Only one has undergone a large-scale clinical trial, only to prove unsuccessful. Currently, two candidate vaccines are undergoing human trials in Thailand and the United States. Nearly half the 39.4 million people infected with HIV worldwide are female. Three-quarters of all HIV-positive women live in sub-Saharan Africa. About 57 percent of the adults with HIV are women.