Why is the COVID-19 case fatality rate unreliable?

Published in El Pais, 18 April 2020 and in Los Tiempos 19 April 2020.

The COVID-19 outbreak fatality rate is calculated as the number of deaths, compared to a related number of infected people. To find out which country is doing “best”, it is tempting to use this indicator, but it is not entirely appropriate.

At best, the fatality rate can be said to depend on: 1) the quality of medical care; thus, the ability to cure infected people and 2) the average age level of those infected. It is already clear that the older the person, the greater the probability of dying. 3) other reasons not yet discovered. In other words, if two countries have the same quality of medical care and age composition, there is no reason for the fatality rate to differ significantly, even if one has many more cases than the other.

The number of cases infected with the COVID-19 virus does not reflect reality. For example, in the Netherlands, hardly anyone gets a Coronavirus test, only when they get to the hospital extremely ill. People with mild symptoms do not get tested and stay home. The main reason is that there is simply not enough test capacity. The Netherlands prefers to use the capacity for severe cases within hospitals. Therefore, the actual number of cases is greater than those reported as “confirmed”. Experts say the real number of cases can be 2 to 6 times higher. Countries with higher testing capacity, such as Germany, will have a higher number of cases and, therefore, a lower calculated case fatality rate. Another aspect to consider is that most of the countries increased their testing capacity in the last days. This might suggest that the number of cases is on the rise, but it is not.

Furthermore, to make a correct calculation of the fatality rate, it is necessary to work with closed cases. For example: 1,000 people are infected, of those 970 are cured and 30 die, so the death rate is 3%. So far, many calculate the case fatality rate with the total number of cases that have occurred, but of these, many are still active and yet will change to cured or deceased. Furthermore, since many countries do not record cured cases, it will be even more difficult to adjust the case fatality rate.

My advice is, be careful when using the numbers to make a statement about the Coronavirus, especially when you oversee developing or influencing the policies of your country or have the important job of reporting as a journalist.

Note after publication:
A good source to see the number of confirmed cases and deaths of all countries check the site of the World Health Organisation: https://who.sprinklr.com/