then you might as well pay for it

99% of closed rooms are owned by somebody. If they are rented out then the responsibility of what happens inside goes to the renter.

Covid 19 gets transmitted in closed rooms.

So it is simple to make the people that house the locus of infection responsible for it. Have them cover the hospital costs of those infected, and those that got infected by them. Just trace the Virus DNA: It is different enough in some details to support these kind of chains.

There will be much less parties and gatherings. Covid would not have an easy way of spreading in the first world as it has now.