Study VX16-661-114 (Study 114) is a Phase 3b, randomized, double-blind, placebo-controlled, parallel-group, multicenter study in subjects aged 12 years and older with CF who are homozygous for the F508del mutation on the cystic fibrosis transmembrane conductance regulator gene (CFTR) gene and who discontinued treatment with Orkambi due to respiratory symptoms considered related to treatment. This study is designed to evaluate the safety and efficacy of Tezacaftor/Ivacaftor (TEZ/IVA).

Inclusion Criteria:

• Willing and able to comply with scheduled visits, treatment plan, study restrictions, laboratory tests, contraceptive guidelines, and other study procedures.
• Prior discontinuation of Orkambi, with at least 1 respiratory sign or symptom considered related to therapy.
• Resolution or stabilization of qualifying event(s) >28 days prior to Screening.
• Discontinuation of Orkambi therapy must have occurred within approximately 12 weeks from the first dose of Orkambi.
• Homozygous for F508del mutation in the CFTR gene as documented in the subject's medical record. If genotype documentation is not available in the medical record, genotyping will be performed during screening.
• FEV1 ≥25% and ≤90% of predicted normal for age, sex, and height.
• Stable CF disease as judged by the investigator.
• Other protocol defined inclusion criteria could apply.

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 subject.
• Recent rapid or progressive deterioration in respiratory status.
• Receiving continuous oxygen at >2L/min or on face-mask ventilation.
• Any protocol-defined exclusionary laboratory values at Screening.
• Child-Pugh Class B or C hepatic impairment.
• An acute upper or lower respiratory infection, pulmonary exacerbation, or change in therapy for pulmonary disease within 28 days before Day 1.
• Documentation of colonization with organisms associated with a more rapid decline in pulmonary status.
• History of lung transplantation since most recent initiation of Orkambi.
• History of alcohol or drug abuse in the past year as deemed by the investigator.
• Participation in an investigational drug study or use of a CFTR modulator within 28 days or 5 terminal half-lives of the investigational drug or modulator (whichever is longer).
• Use of restricted medications or foods within the specified window before the first dose of study drug, or an anticipated need or use of restricted medication or foods after the first dose of study drug.
• Pregnant or nursing females: Females of child-bearing potential must have a negative pregnancy test at Screening and Day 1.
• Other protocol defined exclusion criteria could apply.