The key issue is that as a general principle the time required for a population of microorganisms to die is directly proportional to the size of that population. This means the greater the amount of virus deposited on a surface, the longer you will find viable viral particles on that surface.

So in terms of designing experiments that are relevant to public health, one of the more important variables in these studies is the amount of virus deposited on a surface—and the extent to which this approximates what would happen in the real world.

If you understand this, it becomes apparent that a number of these virus survival studies stacked the odds of detecting viable virus by depositing large amounts of virus on surfaces far in excess of what would be reasonably expected to be found in the real world. What’s more, some of these studies customized conditions that would extend the life of viral particles, such as adjusting humidity and excluding natural light.