Depending on its scale, a biological attack has the capacity to go beyond 'normal' emergency situations and turn into a survival situation. Firstly, as we've already seen, there's every chance that the biological attack will pass by unnoticed for several days or even weeks, giving itself plenty of time to cover a wide geographical region before action begins to be taken. This already makes containment of the disease more difficult.
Then it depends on the disease itself. Is it a common strand of a disease that can be treated with antibiotics? If so, the situation can be normalized in a relatively short period of time. However, if it's a new, more resistant strain of a disease (or a new disease altogether) then treatment may be more difficult or even impossible. In any case, it will take at least 48 hours to determine the qualities of the disease and our ability to treat it.
Even if it's determined to be a common strain of the disease, some vaccinations have been in storage for a long time, and it's not sure that they will still be effective. If not, it can take months or, possibly, years to develop new vaccines. It is this type of scenario that can lead to a sustained crisis and a survival situation.
It is worth noting, that the chances of a crisis escalating to the point where you'll need to spend several months in a survival situation are very slim. However, a crisis that continues for several days or even weeks is possible.
For that reason, it is worth making some preparations in advance. It will put your mind at ease and, if a worst case scenario were ever to develop, you'll greatly increase you and your family's chances of surviving.