Researchers have found that aweak version of the AIDS virus may help protect against the lethal form. A nine-year study of prostitutes in Senegal showed that those infected with HIV-2, the weaker cousin of the HIV-1 virus that causes most AIDS deaths, were 70 percent less likely to contract AIDS.TIME science writer Christine Gormanreports that the findings are encouraging news for scientists seeking an AIDS vaccine. Researchers will now try to isolate the part of HIV-2 that helps the immune system fight off HIV-1. Dr. Phyllis Kanki, who headed the study for the Harvard school of Public Health, cautioned however that the new findings do not mean that "people should go out and get infected with HIV-2 to protect against HIV-1." HIV-2 is also a dangerous virus that can cause cancer.