Uhh... I think, I _hope_ that we are talking about 40% of your workforce NOT SHOWING UP TO THE OFFICE for days or weeks, not dropping dead, not even necessarily getting sick.
During the 1918 Spanish flu epidemic, and estimated 20 to 50 million people died worldwide. Every year, ordinary flu kills between 1/2 and 1 million people. Nobody really knows how many people the next flue pandemic will kill, and they don't really know when it will come. It could be next winter's flu season. Or it could be 10 or 15 years from now. Also, the impact of the flu is not just deaths. Many more people will be sick and will recover. But they won't be able to work. Many people will not be sick but they will want to stay home and care for their sick family members or friends because they know that this time, the flu is a SERIOUS ILLNESS. This is where the figures of 25% to 40% of the population come from. It includes all those who stay home through illness or through the desire to care for an ill person. What can't be predicted is how many will stay home through fear. In any case, if systems are in place to work from home, then the impact is reduced to those who are actually ill. In addition to percentage of people impacted, there is the timeframe. They estimate that the pandemic will last 3 to 5 months. And then there are the actions of local governments. In my city they plan to prohibit sporting events, conferences, theatre performances and similar events which attract crowds. They may shut down the public transport systems in whole or in part. This is where you need to coordinate your company's activities with local governments. Does your company's continuity planning department really know who are the critical people and what support they need? What if somebody needs to go to a PoP to replace cards in a router? Will the police let that person travel? Is that person registered as a critical employee who needs to be supported, not hindered? What if your mayor declares that the police will not allow anyone on the streets without a facemask? Will your critical employees have the facemasks that they need or will the police force them back into their cars at gunpoint? You need to work through various scenarios with your continuity planning people and make sure that they liaise with local officials. Everyone knows that the telephone company is important, but it is not as widely known that Internet infrastructure is as important. --Michael Dillon