The finding that antiretroviral (ARV) drugs reduce the risk of heterosexual transmission of HIV was chosen by Science as the 2011 Breakthrough of the Year.
Science Article
http://www.sciencemag.org/content/334/6063/1628.full
Original Article
M. S. Cohen et al., “Prevention of HIV-1 Infection with Early Antiretroviral Therapy,” N. Engl. J. Med. 365, 493-505 (2011).