Also, spreading of flu during "flu season" is marked by holidays when long distance travel happens. This causes slightly different strains of the flu to be brought into regions where people do not have a natural defense to that strain.
What I find more in more in life is that those that get ahead are doing so by not doing things the right way. We have such a large population now that it seems those at the top have got there because they have done something wrong in order t get there.