H5N1 is already extremely good at spreading between birds, getting better at that is not going to increase its fitness. It's the amount of contact between live

H5N1 is already extremely good at spreading between birds, getting better at that is not going to increase its fitness. It's the amount of contact between livestock & humans that we primarily care about, and that is a lot larger with a large number of small farms than it is with a small number of large farms.