The 45-year fight against HIV is one of humanity’s greatest victories. It’s also in danger.

On June 5, 1981, the Centers for Disease Control and Prevention published a brief, clinical report in its Morbidity and Mortality Weekly Report about five young men in Los Angeles who had developed a rare and deadly form of pneumonia. 

The write-up, barely a page long, ran in between a report on dengue infections among US travelers and an assessment of measles cases. No one who read it could have known this was the opening chapter of the deadliest infectious disease epidemic since the 1918 flu ...