['cystic fibrosis']
['vx-661', 'ivacaftor', 'placebo matched to vx-661', 'placebo matched to ivacaftor']

        Inclusion Criteria:

          -  Homozygous for the F508del CFTR mutation

          -  FEV1 ≥40% and ≤90% of predicted normal for age, sex, and height

          -  Stable CF disease as judged by the investigator

        Exclusion Criteria:

          -  History of any comorbidity that, in the opinion of the investigator, might confound
             the results of the study or pose an additional risk in administering study drug to the
             participant

          -  Pregnant and nursing females: Females of childbearing potential must have a negative
             pregnancy test at screening and Day 1 of the PC Phase and Day -7 or Day 1 of the OLE
             Phase (whichever was applicable)

          -  Sexually active participants of reproductive potential who are not willing to follow
             the contraception requirements

          -  The participant or a close relative of the participant is the investigator or sub
             investigator, research assistant, pharmacist, study coordinator, or other staff
             directly involved with the conduct of the study.
      