There is much debate about whether COVID-19 may have moved from the pandemic to the endemic phase, with many thinking that ‘endemic’ would mean a return to ‘normality’ and the threat gone. This is a misunderstanding of what ‘endemic’ means. Endemic infectious diseases result in high death tolls that often exceed those caused by epidemic or pandemic outbreaks, and endemic pathogens can require the same restriction measures as epidemics and pandemics caused by newly introduced infectious agents. By Martin Michaelis and Mark Wass.
In the current public discourse, the term ‘endemic’ is often used to signal the end of the COVID-19 threat and as a sign that we can return to (pre-pandemic) normality.
This is based on a misconception. The terms epidemic and pandemic describe the rapid spread of pathogens. While epidemics are limited to certain (potentially very large) regions, pandemics affect the whole world.
The term ‘endemic’ is not a contrast to the terms ‘epidemic’ or ‘pandemic’. It simply means that there is a constant baseline level spread of a pathogen in a population that does not depend on an external input.
Endemic pathogens are not necessarily ‘mild’ nor ‘self-limiting’. Endemic viruses can cause large pandemics, as exemplified by the Spanish Flu that was caused by an influenza virus, although influenza viruses are anticipated to have been endemic in the human population for thousands of years.
Tuberculosis (caused by a bacterium, Mycobacterium tuberculosis) is an endemic disease estimated to be responsible for approximately 1.5 million deaths each year. Endemic smallpox viruses were associated with a mortality rate of about 30% and are thought to have killed about half a billion people in the last 100 years of their existence prior to their eradication by a vaccination programme. Endemic measles viruses caused an estimated 2-4 million deaths each year, before large vaccination campaigns were introduced.
So far, control measures against COVID-19 have been introduced, when our hospital capacities were at a point, where the continued, unhampered disease spread would have overwhelmed our health care capacities, such that further unhindered COVID-19 spread would have seen patients needing treatment being turned away from hospital. Hence, the COVID-19 control measures were necessary to ensure that everybody in the UK in acute need of medical treatment actually received this treatment.
Hence, the introduction of control measures is independent of whether a pathogen is endemic or not. If the number of severely ill COVID-19 patients rises again to a level beyond the available healthcare capacities, restrictions will have to be introduced again, independently of whether COVID-19 is an endemic disease or not. And currently, there is no reason to believe that there will not be further COVID-19 waves.