Under this definition, it's within the realm of possibility that I could win the Mega-Millions lottery this week, that a large meteor could hit the earth within the next several years, or that the Boston Red Sox could win the World Series in my lifetime (whoops, strike that last one).
The real question for serious people is: what are the actual odds of such a cataclysmic event happening? Five percent, once percent, .001 percent? Without this kind of perspective, it moves from the realm of the serious to mere fearmongering. Medicine has advanced just a little bit since 1918.
I'm not an oddsmaker, but I am a "serious" person. A world-wide Flu pandemic can happen and will likely happen at some point in time. It will take some time for the deadly genetic shift to occur (proven cases of the human-to-human bird flu infection have been documented over the past 5 years). A wide-spread pandemic could happen this winter, or at any point in the future. This event can't be predicted.
Every year the CDC tries to predict the Flu strains coming for the next winter season and these strains are formulated into the next vaccine. However, they are not always right in their selection. The current 2004/2005 flu vaccine would have limited or no effect on a "bird" flu pandemic.
You are correct that medicine has avanced in the past 86 years. Because the US and the industrialized world will have access to the newer anti-viral medications, mortality rates can be controlled to some extent in the event of a Flu pandemic. However, in the less developed parts of the world that may not have full access to these medications, there could be a death rate of epic proportions.
Agsin, infectious diseases such as Inflenza that have the potental reach to kill 100's of millions in a matter of weeks should be taken very "seriously". This is not "fearmongering". This is reality!