It is interesting to consider what would have happened if the Covid virus had emerged in 1921. Or 1821. Or 1521. There would have been no vaccine, for one thing. Treatment would mostly have been worse. In the 17th century we would have blamed the entire thing on Catholics. But in a few respects, bizarrely, we might have done better. For instance, miasma theory, although technically wrong, might have protected us better against airborne transmission than the early scientific consensus that the disease was spread via droplets on surfaces. A believer in miasma theory might have practised mask wearing (ideally with a large beak), indoor ventilation and outdoor gathering more assiduously than we did. You can see the benign influence of this theory in the design of many large-windowed, lofty Victorian buildings, and in the heroic success of 19th-century sewage projects.