https://issuesinsights.com/2020/03/03/were-accumulating-more-critical-information-about-the-coronavirus-every-day/
With cases of the new coronavirus (officially SARS-CoV-2, and the illness it causes designated COVID-19) spreading, there is intense interest in what we know and what we can expect. Here’s a primer.
There are several factors that determine how damaging and worrisome outbreaks will be. The first is the degree of infectiousness, or ability to spread. Examples of the extremes are noroviruses, which can sweep rapidly through an institution or cruise ship, and the rabies virus, which is almost always transmitted to humans through the bite of a warm-blooded animal.
The second is virulence — the severity or degree of pathogenicity of the infection. Using the same two examples as above, norovirus infections cause severe nausea, vomiting, and diarrhea, but the symptoms are short-lived and almost never cause significant morbidity if treated symptomatically. Thus, although high in infectivity, they are low in virulence. By contrast, by affecting the brain, rabies gives rise to central nervous system symptoms and is almost always fatal once symptoms occur.
Not surprisingly, the most worrying events are a combination of high levels of both infectiousness and virulence. An example of that would be flu in a bad year — one in which the vaccines aren’t a good match for the viruses circulating in the population, which gives rise to high numbers of illnesses, hospitalizations, and deaths. This flu season in the Northern Hemisphere is looking like a pretty average one; the Centers for Disease Control and Prevention estimates that so far this season there have been at least 32 million flu illnesses, 310,000 hospitalizations and 18,000 deaths from flu. And those figures are in spite of pretty effective vaccines — again, about average, at 45%.
