well the SARS outbreak only killed maybe 30-40 people but it did a number on Torontos economy as well as the rest of Canada not to mention Hong Kong.
Even here in Vancouver people stayed away from public events and restaurants in droves. It was definitely felt in the economy, even though a small number of people were affected.
Of course you may talk about the odds being low, Im sure the people of New Orleans would have said the same thing before Katrina hit.
While I wouldnt worry about it too much It doesnt hurt to plan, and Id damn well have the CDC prepare flu vaccines etc. for an outbreak that may not occur even though it may cost 5 billion dollars, because if it comes and theyre not prepared - its going to cost a lot more than that.