Investigators observed samples from 84 naturally influenza-infected individuals and found increased levels of cytokines MCP-3, IFNa2 and plasma IL-10 predicted progression to more severe flu symptoms. While increased levels of plasma IL-10, MCP-3 and IL-6 levels predicted hospitalization. The findings from this paper also explain why infants are at high risk for complications, and why the benefits from antiviral drug oseltamivir are short-lived.