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5. HIV Treatment as Prevention: No Infections in PARTNER Study

Pre-exposure prophylaxis (PrEP) for HIV negative people was the biggest topic in HIV prevention in 2014, but use of antiretroviral therapy by HIV positive people to prevent onward transmission of the virus -- dubbed treatment as prevention or TasP -- also received further support.

At the Conference on Retroviruses and Opportunistic Infections in March, Jens Lundgren's team reported findings from the PARTNER study showing that no cases of linked HIV transmission were seen during 44,500 condomless sex acts by more than 750 heterosexual and gay male couples.A statistical analysis suggests that the maximum likelihood of transmission via anal sex from someone on ART with an undetectable viral load is 1%-4% per year, but according to PARTNER co-investigator Alison Rodger, "Our best estimate [of the chance of transmission] is it's zero."

NEXT: 6. HIV Drugs: Few New Approvals, but Pipeline Looks Promising