“How lethal are H5N1 influenza viruses to humans? The answer to this question is central to the current debate over research on genetically modified H5N1 viruses. In an effort to determine if highly pathogenic avian influenza H5N1 was capable of becoming easily transmissible between mammals, researchers in the Netherlands modified H5N1 viruses to make them transmissible between ferrets. The research has not yet been published, but reportedly the viruses were highly lethal to the ferrets when directly instilled into the ferrets’ trachea. Since ferrets are commonly used as the best animal model for simulating human influenza infection, concern has been raised that the newly modified virus may be highly lethal and highly transmissible among people as well. Some proponents of the research argue that the H5N1 viruses are not as dangerous as they seem and that therefore concerns about an accidental release of the mutated virus or its intentional use as a weapon are overblown. Critics of the research argue that the currently circulating strains of H5N1 are extraordinarily lethal and that research with highly lethal viruses modified to be highly transmissible poses an unacceptable risk to society. In an attempt to shed light on this question, we review the available evidence.”

by Eric S. Toner and Amesh A. Adalja