Humana reported $1.2 billion in first quarter net income as the company gets better control of medical cost trends in its Medicare Advantage plans.

Health insurer Humana on Wednesday reported lower-than expected medical costs in the first quarter, allaying investor concerns about the sector after bellwether UnitedHealth's disappointing financial results earlier this month.

Despite the outperformance, the payer’s stock was largely flat following the earnings release — a market reaction that reflects the uncertainty facing Humana.