What would be the economic impact of an outbreak on our society caused by influenza epidemic and pandemics? 

I agree with the above post in that a true pandemic of a
deadly strain of flu virus could lead to the worst case scenario described in the first
post.

If you look at last year's Swine Flu scare, which
some described as a pandemic, the economic effects were more subtle.  According to the
Centers for Disease Control in Atlanta, about 20 million Americans per year get the flu,
and the disease takes between 3 - 5 days to run its course under normal circumstances. 
Assuming that even 60% of those infected are members of the workforce, we would be
looking at 36 - 60 million lost work days.  So one economic impact is that we lose
productivity, and medical costs rise as a result of the
illnesses.

Since government routinely provides or contracts
for the production of vaccines, there is a significant up front cost to taxpayers to
vaccinate even the most vulnerable people in our population, the young and the
elderly.