A mutation has made the H7N9 avian influenza virus more resistant to antiviral drugs, yet it is no less transmissible, according to new research. Often, antiviral resistance is coupled with a loss in the ability to spread. Meanwhile, the World Health Organization has reported four new confirmed cases in China. Although two of the patients are members of the same family, the WHO maintains human-to-human-transmission is not sustained by the virus at this time, and the authors of the new study agree. "It's important to emphasize that these H7N9 viruses seem to transmit fairly inefficiently overall," said researcher Nicole Bouvier.