A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Study to Evaluate the Efficacy and Safety of VX-661 in Combination With Ivacaftor

This is a Phase 3, randomized, double-blind, placebo-controlled, parallel-group, multicenter
study in people with CF who are homozygous for the F508del-CFTR mutation. This study is
designed to evaluate the efficacy and safety of VX-661 in combination with Ivacaftor (IVA,
VX-770). The active treatment regimen comprised of a morning dose of a fixed-dose combination
(FDC) tablet of 100 milligram (mg) VX-661/150 mg IVA once daily (qd) and an evening dose of
IVA 150 mg to be taken approximately 12 hours after the morning dose. The placebo regimen was
visually matched tablets to be taken with the same schedule as the active treatment.

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