A lot more people travels globally than it used to. Even if the disease is not a whole lot worse than other known flu varieties, it can spread wider and faster because human hosts travel a lot these days.
It is possible that more virulent strain can evolve from the current one if the disease can be spread so widely due to its hosts' behavior. There is a research done on this topic. If human hosts are relatively isolated, virulent strain cannot survive among host population for long. But if they are not, more and more virulent strain can evolve because while one host dies, others will pick it up from the dying host. The disease will stay in the population, preying on new hosts, while it is killing old hosts. The faster the spread of the disease, the more likely is the disease to turn virulent and still survive among the host population.