The purpose of this study is to learn more about the long-term safety, tolerability, and effects of the combination of VX-661 and ivacaftor in subjects with Cystic Fibrosis. This is a rollover study from study VX 15-661-113 Part B. Approximately 121 people will participate in this study. Participation could last for approximately 100 weeks. This will include a treatment period that will last up to 96 weeks, and a follow-up period that will last up to 4 weeks.
This is an observational study which will collect sweat chloride values from approximately 1000 cystic fibrosis subjects who are currently on cystic fibrosis transmembrane conductance regulator (CFTR) modulators. This study will require one visit to an MUSC clinic which will last approximately 2 hours. Compensation is provided.