A New York Times opinion piece from a mathematician…
…points out that both the numerator and the denominator of the case fatality rate — the number of deaths and the total number of people infected — may be deceptive. Ascribing causes of death can be tricky, with both false positives and false negatives. And various factors make for inaccuracy in the total number of infected people. Some are treated without having been formally tested. Some may be infected but showing no symptoms, including those still in the lengthy incubation period of the virus.
Further distortions are created by the way these numbers are determined by medical officials and presented by the media. Definitions of infection have been changed on the fly, causing immediate and misleading statistical — but not real — shifts. Underreporting may be deliberate, for policy reasons, or more mundane, e.g. due to changes in the availability of test kits. A dramatic increase in daily deaths may seem ominous but, in context of an increase in the number of newly infected people over the same interval, may actually represent lower lethality than previously thought.
These uncertainties point out the limitations of “constant on-the-nose” reporting of statistics, a “shortsighted approach that’s difficult to resist.”
As of Tuesday, the case fatality rate of COVID-19 appeared to be about 2.5 percent. That’s in keeping with what it was, for example, from the beginning of the outbreak up to Jan. 28. By comparison, the case fatality rate for the seasonal flu in the United States ranges between 0.10 percent and 0.18 percent. For SARS, it’s about 10 percent and for MERS, about 35 percent. For Ebola, it has varied between 25 percent and 90 percent, depending on outbreaks, averaging approximately 50 percent.
And so based on what we know so far, COVID-19 seems to be much less fatal than other coronavirus infections and diseases that turned into major epidemics in recent decades. The operative words here are “based on what we know so far” — meaning, both no more and no less than that, and also that our take on the situation might need to change as more data come in.
Remember, too, that even if only a small percentage of the people infected with COVID-19 die in the end, the death toll in absolute numbers could still be dreadful if the total population of infected turns out to be very large.