Any subject who is randomized into Part A or Part B may consent to take part in a 12-month Extension Period. Before any study-related procedures are performed, the subjects will have all study procedures explained to them, including information regarding the nature of the study, and subjects must sign an informed consent/assent form. During the Extension Period, subjects will receive tenofovir and return for visits every 3 months for follow-up safety and efficacy assessments.