The pandemia of COVID–19 has severely hit our world. Many attempts have been made to predict its course since beginning of the outbreak. Basic epidemiological data such as the numbers of confirmed cases, of deaths, of recoveries, and of tested individuals are readily accessible, even to the public. Despite this, most of the classic prediction models have failed. These failures have several reasons: the application of lockdown at different times within the countries of the world, the inconsistent selection of the population for testing, and the low sensitivity of the employed tests (PCR or ELISA) resulting in false-positive and false-negative results. The last-mentioned problem means that both a patient who is actually infected with COVID–19 and one who is COVID–19-free can receive a positive or negative result after the test. Additionally, the sensitivity of the tests varies during the phase of the disease. Death may appear to be a good epidemiologic factor. Unfortunately, this is not the case for the COVID–19 infection. Many patients have died who were positive for COVID–19 but not because of COVID–19, and of course, not all patients who have died have been tested for COVID–19. All of these above-mentioned factors have made the construction of prediction models extremely difficult.
The survival of patients with a severe COVID–19 course is considered to be mainly dependent on access to mechanical ventilation. Because of the well-known exponential growth of confirmed cases and deaths, state and health authorities began to feel afraid of the lack of ventilators in their hospitals as the pandemic progressed. For example, Prof. Dr. Thomas Van Boeckel from the Department of Environmental Systems Science at ETHZ suggested that Switzerland would run out of intensive care beds on April 2 as a result of the progression of the coronavirus pandemic (1). The opinions of other authorities around the world were similar. As we now know, the system did not collapse. However, why did it not happened, and do we still run the same risk?