This research has all led to a significant shift in how HIV prevention and treatment are approached as public health issues. In the virus’s early days, when HIV infection was likely to lead to AIDS-related illnesses and death, most public service messages offered dire warnings against unprotected sex and encouraged regular HIV testing among those at risk. As medical advances made HIV more manageable, the warnings continued—but for those who had become infected, new messages stressed the positive outlook. HIV was no longer a death sentence, and people who were infected could live healthy lives with treatment.

Advances in research also led to the discovery that people who are HIV-negative could take the same medications used to treat people with HIV and thereby resist becoming infected themselves. A drug called Truvada, manufactured by Gilead, was approved for use to treat people who were infected with HIV in 2004. Subsequent tests found it was also effective in preventing the virus’s spread when taken by those who were not infected but were sexually active with those who were. In 2012, Truvada was approved as a form of pre-exposure prophylaxis (PrEP)—a preventive medication for those in high-risk categories.

We’re now seeing a new public health approach, one designed to push HIV-positive people to seek treatment by helping them understand that this will actually stop them from infecting others. The campaign’s message is “undetectable=untransmittable,” or “U=U” for short. It simply means that if an HIV-positive person’s viral load has been suppressed enough through treatment that it doesn’t show up in blood tests, then that person is unable to infect others. The treatment for HIV is also the mechanism to prevent the spread of HIV.