My observations are noticing that population density is a huge factor for CV, not just due to increased chance of exposure but also to intensity or "dose" of exposure. Here is an excerpt from a New Yorker article discussing effect of higher dose:
"Perhaps the strongest association between the intensity of exposure and the intensity of subsequent disease is seen in measles research. “I want to emphasize that measles and covid-19 are different diseases caused by very different viruses with different behaviors,” Rik de Swart, a virologist at Erasmus University, in Rotterdam, cautioned when we spoke, “but in measles there are several clear indications that the severity of illness relates to the dose of exposure. And it makes immunological sense, because the interaction between the virus and the immune system is a race in time. It’s a race between the virus finding enough target cells to replicate and the antiviral response aiming to eliminate the virus. If you give the virus a head start with a large dose, you get higher viremia, more dissemination, higher infection, and worse disease.”
The higher the population density the greater dose that contracters of the virus will be likely to receive. And the greater the dose the more likely the fatality.
High density population also works in conjunction with air pollution as an amplifier for severity of the virus. The denser the population, the more ozone pollution and the more people with compromised or damaged respiratory.
I think the big story that is going to come out of this is how this virus's lethality was tailor made for huge urban centers with sardine packed transit and inner city poverty and pollution related health issues.
