Different perspectives on COVID-19’s attack rate

The attack rate of an infectious disease is the % chance that you contract it. I think it is term was introduced by epidemiologists. A high attack rate is bad of course, a lower one would be better, so we want to know what the attack rate depends on. Epidemiologists typically want to know how the attack rate depends on, for example, “age, symptom status, duration of exposure and household size” — see a recent preprint by Prof Neil Ferguson at Imperial College and coworkers. So here the questions are: Are children more likely to become infected than the elderly? Does longer contact with an infected person increase the chance of infection? And so on. Aerosol scientists such as Prof Jose Jimenez, and at least some medics, have a different perspective on what determines the attack rate. Prof Jimenez has a Google Sheets that estimates attack rates. But here the assumption (not question) is that the attack rate depends on duration, but not age, as well as on other factors such as ventilation. I am wondering about these two different perspectives on the same problem.

I am genuinely not sure if these very different perspectives on essentially the same problem, are complementary or contradictory. Both epidemiologists and aerosol scientists basically start with epidemiological data, i.e., data for the attack rate in various situations, but I think epidemiologists get as much data as possible and look for correlations. Whereas, the aerosol-science perspective is to include a physical model of how the virus actually gets from the infected person to the person who becomes infected. For example, to put in physical intuition that more air ventilation will dilute the virus and so reduce the attack rate.

I think epidemiologists are often interested in how the attack rate depends on demographic information, such as age, gender, and so on, which is perhaps why governments often call on epidemiologists. If a government wants a prediction of a national mortality rate, an epidemiological model plus their country’s demographics, will be be able to do this.

But we as individuals can’t change our demographic info; I am a middle-aged white man and I can’t do anything about that. But improving ventilation, and wearing a mask, are things I can do, and these recommendations come (mostly) from aerosol and other scientists, not epidemiologists. So maybe as individuals we should pay more attention to aerosol and similar scientists.

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