In this sub-study of a randomized clinical trial of hospitalized patients with MERS, we demonstrated that treatment with interferon-β1b and lopinavir–ritonavir treatment was associated with lower 90-day mortality among patients with lower, but not higher, cytokine levels at trial enrollment (specifically IL-2, IL-8, and IL-13), and among patients who were treated early. The gene discussed is CXCL8; the disease is Middle East respiratory syndrome.