On June 5, 1981, the CDC identified a cluster of five cases of a rare pneumonia occurring in previously healthy young, homosexual men in the US. Forty years later, despite great advances in therapies for prevention, and extending life expectancy and quality of life, the pandemic is still growing in some places and killing millions around the world. Epidemiologist Dr. Chris Beyrer, associate director of the Johns Hopkins Center for AIDS research, talks with Stephanie Desmon about the work that still needs to be done, what we’ve learned from the AIDS pandemic, and how we need to apply these lessons to the global COVID-19 response.