COVID-19's lethality provides a grim opportunity to track its spreadCOVID-19 is different from the viral epidemics of the recent past in a few ways: it is more widespread than severe acute respiratory syndrome, more infectious than seasonal influenza and has killed more people than Ebola.
And it is different in the way that epidemiologists are tracking its progress. Instead of relying principally on the number of infections, or the ratio of deaths to infections—known as the case fatality rate—researchers are looking at the daily deaths attributed to COVID-19 to monitor the impact of the disease and to guide responses.
In part, that\'s due to a lack of testing in many countries and the virus\'s ability to spread in people who don\'t show symptoms—both of which make counting the number of infections very difficult. COVID-19 has also been more fatal than many recent epidemics, which makes its death toll relevant to understanding the pandemic more broadly.
COVID-19 is not deadly to most people: the World Health Organization estimates that it is fatal in about 3.4% of reported cases, and the risk of death varies by age group and a host of other factors. But the pandemic is now widespread enough that the reported number of deaths within a country, day by day or week by week, is a surer tracker of the disease\'s progress and effectiveness of containment than are other measures. When the rate of new deaths per day starts to slow or reduces, it\'s a good sign that the disease has peaked, and several countries are seeing early signs that this is happening.