After several months of delay, the research groups of Erasmus MC, led by Ron Fouchier, and Cambridge University, led by Derek Smith, today published their research on the transmissibility of avian H5N1 influenza virus in the special issue on H5N1 virus in the leading scientific journal Science. The publication by Herfst et al. shows that only a small number of mutations are necessary to change the H5N1 virus so that it can spread between mammals via respiratory droplets. The publication by Russell et al. shows that it might be possible for human-to-human airborne transmissible avian H5N1 influenza viruses to evolve in nature. The research presented in these publications was partially funded through EMPERIE and ANTIGONE.