Placebo matched to VX-661

Study of VX-661 Alone and in Combination With Ivacaftor in Subjects Homozygous or Heterozygous to the F508del-Cystic Fibrosis Transmembrane Conductance Regulator(CFTR) Mutation

Study to Evaluate Safety and Efficacy of VX-661 in Combination With Ivacaftor in Subjects With Cystic Fibrosis, Homozygous for the F508del-CFTR Mutation With an Open-Label Expansion