A 55-year-old male with type 2 diabetes presents for a follow-up psychiatric appointment. He was started on sertraline 50 mg daily 8 weeks ago for major depressive disorder. His initial PHQ-9 score was 22. Today his PHQ-9 score is 14, and he reports partial improvement in sleep and appetite but continued anhedonia, fatigue, and difficulty concentrating. He denies suicidal ideation. The PMHNP should interpret these results as indicating: