Main Inclusion Criteria: All subjects must meet ALL of the following inclusion criteria to be enrolled. There are additional inclusion criteria.  Male and female subjects aged 18 (or the country specific minimum age of consent >18) years or older. Meet revised 2016 World Health Organization (WHO) criteria for the diagnosis of polycythemia vera and have either JAK2 V617F mutation or JAK2 exon 12 mutation. At least 3 phlebotomies due to inadequate hematocrit control in 6 months before randomization or at least 5 phlebotomies due to inadequate hematocrit control in 1 year before randomization.  CBC values immediately prior to randomization:  Hematocrit <45%, WBC 4000/μL to 20,000/μL (inclusive), and Platelets 100,000/μL to 1,000,000/μL (inclusive) Subjects receiving cytoreductive therapy at randomization must be on a stable PV therapy regimen. Subjects treated with phlebotomy alone at randomization must have stopped cytoreductive therapy 2 to 6 months before screening.  Main Exclusion Criteria: Subjects must meet NONE of the following exclusion criteria to be enrolled. There are additional exclusion criteria.  Clinically meaningful laboratory abnormalities at Screening. Subjects who require phlebotomy at hematocrit levels lower than 45%. Clinically significant thrombosis (e.g., deep vein thrombosis or splenic vein thrombosis) within 2 months prior to randomization. Active or chronic bleeding within 2 months prior to randomization. History of invasive malignancies within the last 5 years, except localized cured prostate cancer and cervical cancer. Subjects with non-invasive non-melanomatous (e.g., squamous cell or basal cell carcinoma) skin cancer during screening unless adequately treated before randomization. Received Busulfan, Pipobroman or 32Phosphorus within 7 months prior to screening.