In the final (4th) installment of the series based on “Tomorrow Is a Long Time: Tijuana’s Unchecked HIV/AIDS Epidemic,” writer Jon Cohen explores what it would take to end the AIDS epidemic in Tijuana by 2030, as called for by UNAIDS. Dr. Davey Smith of UC San Diego argues for aggressive, frequent HIV testing in high-risk groups and shows how cutting-edge genetic science can unravel how the virus moves through communities. Cohen explains the benefits of harm reduction strategies, such as providing clean needles and methadone to thwart HIV transmission. And, in an intervention tailored specifically to this epidemic, Steffanie Strathdee and Tom Patterson’s group at UC San Diego has begun training the Tijuana Police about HIV and urging officers to see drug addiction as a sickness, not a crime.