Study population and baseline testing prior to enrollment
Eligible participants were 16–21 years of age, HIV-negative per rapid test at screening and enrollment, not pregnant at screening or enrollment, using effective contraception for at least two months prior to enrollment (for those not on contraceptive at screening, the study offered effective contraception at screening, encouraging long-acting contraceptives), and healthy based on physical exam, pelvic exam and laboratory testing. Pregnancy and breastfeeding were exclusionary because the ring had not yet been studied in in an African population of this age. There were no other criteria related to sexual behavior or HIV vulnerability.