Supporting Adolescents to Adhere - an Intervention Using Airtime Rewards Allocated by a Prize Drawing

* For Group 1 (lottery reward with fixed target): Study coordinators check participant's MEMS extraction for last month's adherence. Study coordinators then tell participants of the participants' adherence in the last month. Participants are also informed that during the next clinic visit, if they adhere at least 90 percent they have a chance to enter into a game where they have a chance of winning mobile airtime, by drawing into a bag and picking a card associated with their airtime winnings. If they do not have 90% adherence, they will not receive the airtime award game, but there will be another chance the next time they come for their scheduled clinic visit during the study period. * For Group 2 (lottery award with own target): Study coordinators check participant's MEMS extraction for last month's adherence. They inform participants of their adherence in the last month. In order to be eligible for an airtime reward game, during their next clinic visit they must reach their own target goal. The target adherence goal must be greater than 80%. Participants may, for example, choose 80%, 85%, 90%, 95%, or 100%. Again, if they meet or exceed this target they have a chance to draw into a bag to win mobile airtime. If they do not have meet this self-imposed target adherence, they will not be eligible to play the airtime award game, but there will be another chance the next time they come for their scheduled clinic visit during the study period. During each clinic visit, participants will have their MEMS extracted and study coordinators will check for average adherence between that day and the last clinic visit. For those who have met the target, coordinators will initiate the lottery, complete the drawing procedure, or send them the airtime reward without drawing (depending on which group). Every Sunday, study investigators will send treatment participants a motivational message to remind them about the reward. Within each of the two intervention groups, study investigators will randomly send the message either in a loss-frame or a gain-frame, i.e. an intervention participant (in either group) will some weeks receive a message telling them to keep up motivation (as a code-word for adherence) to win a prize, and some weeks telling them to make sure not to lose their chance to win a prize.