Participants will receive treatment over a 2-year period followed by a 1-year blinded (masked) withdrawal phase. Participants will be provided with anti-allergic rescue medications (antihistamine, topical intranasal corticosteroids, and short-acting beta agonists) throughout the study. Clinical endpoint assessments will be performed at prior to initiating their assigned treatment, after 1 and 2 years of treatment, and after the 1-year withdrawal period at 3 years.