Flu is a very real threat. If this strain does not cross the
species barrier, there is always the next one. And the one after that, .... Sooner or later there will be another large epidemic such as happened in 1918. In the developed countries, things will probably not be as severe as in 1918 because of improved technology and other public health measures. In the undeveloped countries, things will likely be much worse.
Evolution includes continuous wars between pathogens and hosts. The stakes are high.