ETHICAL APPROVAL
The authors confirm that the ethical policies of the journal, as noted on the journal’s author guidelines page, have been adhered to. All animal experiments were approved by the Jiangsu Administrative Committee for Laboratory Animals (Permission number: SYXK-SU-2007-0005), and complied with the guidelines of Jiangsu laboratory animal welfare and ethics of Jiangsu Administrative Committee of Laboratory Animals. Experiments involving live H7N9 viruses were performed in animal biosafety level-3 facilities, which were approved by the Ministry of Agriculture and Rural Affairs of the People’s Republic of China.