A Study to Evaluate the Efficacy and Safety of VX-661 in Combination With Ivacaftor in Subjects Aged 12 Years and Older With Cystic Fibrosis, Heterozygous for the F508del-CFTR Mutation

A Phase 3, Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study to Evaluate the Efficacy and Safety of VX-661 in Combination With Ivacaftor in Subjects Aged 12 Years and Older With Cystic Fibrosis, Heterozygous for the F508del-CFTR Mutation and With a Second CFTR Mutation That Is Not Likely to Respond to VX-661 and/or Ivacaftor Therapy (F508del/NR)

Study to evaluate the efficacy of VX-661 in combination with ivacaftor (IVA, VX-770) through Week 12 in participants with cystic fibrosis (CF) who are heterozygous for the F508del mutation on the CF transmembrane conductance regulator (CFTR) gene and with a second CFTR mutation that is not likely to respond to VX-661 and/or IVA therapy (F508del/not responsive [NR]).

Inclusion Criteria:

• Confirmed diagnosis of CF defined as a sweat chloride value greater than or equal to (>=)60 millimole per liter (mmol/L) by quantitative pilocarpine iontophoresis.
• Heterozygous for the F508del-CFTR mutation and with a second CFTR mutation that is not likely to respond to VX-661 and/or ivacaftor therapy, genotype to be confirmed via assessment at the Screening Visit.
• Forced Expiratory Volume in 1 Second (FEV1) >=40 percent (%) and less than or equal to (<=)90% of predicted normal for age, sex, and height at Screening 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).
• History of solid organ or hematological transplantation.
• Ongoing or prior participation in an investigational drug study or use of commercially available CFTR modulator within 30 days of screening.
• Pregnant or nursing females.