['cystic fibrosis']
['vx-661 plus ivacaftor combination', 'ivacaftor', 'vx-661 plus ivacaftor combination placebo', 'ivacaftor placebo']

        Inclusion Criteria:

          -  Homozygous for the F508del CFTR mutation, genotype to be confirmed at the Screening
             Visit

          -  Confirmed diagnosis of CF defined as a sweat chloride value ≥60 mmol/L by quantitative
             pilocarpine iontophoresis

          -  Forced expiratory volume at one second (FEV1) ≥40% and ≤90% of predicted normal for
             age, sex, and height during screening

          -  Stable CF disease as judged by the investigator

          -  Willing to remain on a stable CF medication regimen through Week 24 or, if applicable,
             the Safety Follow up Visit

        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, or changes in
             therapy (including antibiotics) for pulmonary disease within 28 days before Day 1
             (first dose of study drug)

          -  Pregnant or nursing females (females of childbearing potential must have a negative
             pregnancy test at Screening and Day 1)

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