Burden can be of different kinds: economic cost (at large), death, short term disabilities, long term disabilities, unemployment, health system collapse, etc., but also fear, mistrust, anxiety, loneliness, divorces, civic unrest, etc.
There are many papers that give different numbers for different burdens for different countries but I am not an expert. I could provide you with numbers like la Tuque bellow, but I feel the confidence interval is to big at the moment.
BTW, apparently, there is a sharp increase of poaching of rare species in different countries because there are no toursists... (so another kind of unexpected burden, if we extrapolate)