have found the tenofovir/emtricitabine combination to be over 90% effective at preventing HIV transmission between sexual partners. Treatment as prevention Treatment as Prevention (often abbreviated as TasP) is the practice of testing for and treating HIV infection as a way to prevent further spread of the virus. Those having knowledge of their HIV-positive status can use safe-sex practices to protect themselves and their partners (such as using condoms, sero-sorting partners, or choosing less-risky sexual activities). And, because HIV-positive people with durably suppressed or undetectable amounts of HIV in their blood cannot transmit HIV to sexual partners, sexual activity with HIV-positive partners on effective treatment is a form of safe sex (to prevent HIV infection). This fact has given rise to the concept of "U=U" ("Undetectable = Untransmittable"). Other forms of safe sex Other methods proven effective at reducing STI risks during sexual activity are: Immunization against certain sexually-transmitted viruses. The most common vaccines protect against hepatitis B and human papilloma virus (HPV), which can cause cervical cancer, penile cancer, oral cancer, and genital warts. Immunization before initiation of sexual activity increases effectiveness of these vaccines. HPV vaccines are recommended for all teen girls and women as well as teen boys and men through age 26 and 21 respectively. Limiting numbers of sexual partners, particularly casual sexual partners, or restricting sexual activity to those who know and share their STI status, can also reduce STI risks. Monogamy or polyfidelity, practiced faithfully, is very safe (as far as STIs are concerned) when all partners are non-infected. However, many monogamous people have been infected with sexually transmitted diseases by partners who are sexually unfaithful, have used injection drugs, or were infected by previous sexual partners. The same risks apply to polyfidelitous people, who face higher risks depending on how many people are in the polyfidelitous group. Communication with sexual partners about sexual history and STI status, preferred safe sex practices, and acceptable risks for partnered sexual activities. Engaging in less-risky sexual activities. In general, solo sexual activities are less risky than partnered activities. Sexual penetration of orifices (mouth, vagina, anus) and sharing body fluids (such as semen, blood, vaginal fluids, and rectal mucus) between sexual partners carry the most risk for STIs. Regular STI testing and treatment, especially by those who are sexually active with more than one casual sexual partner. It is possible to attain and show proof of STD-free-verification through online