You may wonder why I post so many research summaries and data analyses. To understand how the epidemic is developing and what appropriate public policy should be, you have to be focused on some key characteristics. For an infectious disease epidemic two things are key. One is how many people might become infected and the other is how serious the disease outcomes are. Since we are in the middle of the epidemic, information is becoming available or generated every day that may be relevant to those big picture issues and people are modeling, of course, the future based on the current data. In a couple of years, and it will take that long for really solid retrospective analyses of incidence and prevalence and real causes of death, etc., we will have a very good picture of the epidemic’s course.
So what I see as I read all this research and look at the data is what you read in my commentary-oriented posts. In terms of number of people infected, it is apparent to me, and should have been to all the public health and epidemiologic experts, that a lot of people don’t get infected or have very mild illness. The range in susceptibility is wide and only a few people have any risk of serious illness or death. Why? Well, the research is now becoming clearer that this is likely due to immune defenses from previous infections with other coronavirus strains. So on issue one, it is highly likely that only a fraction of the population is susceptible to infection and a much smaller fraction is susceptible to serious illness. This has obvious relevance to how much of the population can actually be transmitters and when population immunity occurs and that is enormously significant for public policy decisions.
On the second issue, how serious is the disease, particularly in terms of hospitalization and deaths, it has been clear from the beginning that there is a wide bifurcation in consequences. For the general population, the risk is low, it really is akin to or less than a serious flu year and there is minuscule risk to children and young adults. For the infirm elderly and some people with serious pre-existing illness, it is a very different story. The risk for these groups is high. In Minnesota, 81% of deaths are occurring among residents in congregate living settings, mostly the very old, and 98% of deaths involve pre-existing conditions. This bifurcation of risk also leads to obvious public policy conclusions in terms of what measures need to be taken to protect a population.
In just the last couple of weeks, there is a clear trend in the modeling papers to recognize that variability in susceptibility to infection and serious illness needs to be taken into account and there is another trend of studies finding cross-reactivity in immune defenses to coronavirus, which is the likely primary explanation for the variability in susceptibility. So I will keep tracking as much as I can and we will see what else develops. One item I am watching very closely is the possibility of seasonality.