Covid measures metaphor: Think of each measure (masks, distance, limiting crowds, ventilation, etc.) as a slice of Swiss cheese. Sure, there are holes in each slice, but you stack them together and they cover each other’s gaps.
A Swiss cheese approach to pandemic safety
Also, a nice visual display of how coronavirus spreads in indoor scenarios and how different actions reduce the risk.
A room, a bar and a classroom: how the coronavirus is spread through the air