TNF and influenza: Although patients with severe influenza induced by the H1N1 and H5N1 viruses develop a “cytokine storm,” including high levels of serum IFN-γ and TNF-α, which are commonly associated with rapid progression and poor prognosis [11, 19, 20], we did not detect abnormal levels of serum IFN-γ or TNF-α in patients with H7N9 virus infection.