Mice are a good model for evaluating the pathogenesis and antiviral therapy of influenza pneumonia, due to the general fidelity of the illness in mice to the human disease [16] . Moreover, a mouse model of ARDS caused by highly pathogenic H5N1 avian influenza virus infection has been well established [13] . The typical 2009 H1N1 virus, such as A/California/04/2009 (CA/04), can efficiently replicate in mouse lungs without prior host adaptation. However, it only causes moderate lung lesions and no mortality, even when inoculated at a high dose of 10 6 pfu [17, 18] . Thus, such typical 2009 H1N1 viruses may not be able to induce ARDS in a mouse model.