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

        Inclusion Criteria:

          -  Heterozygous for F508del-CFTR and a second allele with a CFTR mutation predicted to
             have residual function

          -  Forced Expiratory Volume in 1 Second (FEV1) greater than or equal to (≥) 40 percent
             (%) and less than or equal to (≤) 90% of predicted normal for age, sex, and height
             during screening

          -  Sweat chloride value ≥60 millimole per liter (mmol/L) during screening OR as
             documented in the participant's medical record

          -  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

          -  An acute upper or lower respiratory infection, pulmonary exacerbation

          -  History of solid organ or hematological transplantation

          -  Ongoing or prior participation in an investigational drug study (including studies
             investigating VX-661, lumacaftor [VX-809], and/or ivacaftor) within 30 days of
             screening

          -  Pregnant and nursing females

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