In a mine -- constricted space of very small volume with forced ventilation -- the conditions would be ideal for getting infected with a very high initial viral

In a mine -- constricted space of very small volume with forced ventilation -- the conditions would be ideal for getting infected with a very high initial viral load. Under these conditions, it is not unreasonable that immunity of any kind (from infection or vaccination) would not be sufficient to prevent symptomatic COVID19 infections.