H5N1 bird flu has been on the public health radar as a potential cause of the next pandemic since 2003, when I first began to study it. It continues to kill millions of poultry every year. The rare human case is still almost 50% deadly, hence the reason for all the worry.

But despite the fact that H5N1 now shows an ability to infect mammals, with cases found in foxes, seals, dolphins, otters, and wild dogs, the number of human cases remains extremely small. In part, that’s because several mutations would have to occur before bird flu could spread from human to human.