Anthem Inc. said it is now projecting losses on its Affordable Care Act plans this year, a turnaround for a major insurer that had maintained a relatively optimistic tone about that business.

Anthem said it now believed it would see a “mid-single-digit” operating margin loss on its ACA plans in 2016, due to higher-than-expected medical costs. It expects better results next year, because it is seeking substantial premium increases.

Anthem’s financial performance on ACA plans had previously been a relative bright spot among major insurers, many of which continue to struggle.

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