A Study to Compare the Efficacy and Safety of Oral Azacitidine Plus Best Supportive Care (BSC) Versus Placebo Plus BSC in Participants With International Prognostic Scoring System Revised (IPSS-R) Low- or Intermediate-risk Myelodysplastic Syndrome (MDS)

Inclusion Criteria: • Participant has a documented diagnosis of MDS according to WHO 2016 classification that meets International Prognostic Scoring System Revised (IPSS-R) classification of low- or intermediate-risk disease (IPSS-R score between 1.5 and 4.5). MDS diagnosis, WHO classification, and IPSS-R risk classification will be prospectively determined by independent central pathology and cytogenetics review, and applicable central laboratory results. • Participant must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2. Exclusion Criteria: * Participants with prior malignancies must have an expected median life expectancy of at least 12 months at the time of inclusion and no active treatment of any sort for at least 24 weeks prior to randomization (including but not limited to immunotherapy or targeted therapy) * Hypoplastic Myelodysplastic Syndrome (MDS) with a marrow cellularity of ≤ 10% * Participants diagnosed with MDS with excess blasts-2 (MDS-EB2) * Prior treatment with azacitidine (any formulation), decitabine, or other hypomethylating agent Other protocol-defined inclusion/exclusion criteria apply