WHO and UNAIDS applaud results from the HPTN 052 trial that show antiretroviral therapy to be 96% effective in reducing HIV transmission in couples where one partner has HIV. "This is a crucial development, because we know that sexual transmission accounts for about 80% of all new infections," said Dr Margaret Chan, WHO Director-General. "The findings from this study will further strengthen and support the new guidance that WHO is releasing in July to help people living with HIV protect their partners."