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A new strain of bird flu identified in China "is one of the most lethal influenza viruses we have seen so far," Dr. Keiji Fukuda, the World Health Organization (WHO)'s Assistant Director-General for Health Security, tells journalists at a press conference in Beijing on Wednesday.
A four-year-old boy living in a village near Beijing has been confirmed as one the carriers of a deadly strain of bird flu virus. Until the weekend, the outbreak had appeared to be confined to Shanghai and other eastern areas but now it's spread to central and northern China. NBC's Ian Williams reports from Beijing.
Dr. Jeffrey Shaman, Columbia University, tells NBC's Robert Bazell why flu comes in the winter and if the weather has anything to do with it.