Coronavirus: The most important technical terms for Covid-19 – knowledge

Epidemiologists occasionally say: You can drown in data and still thirst for information. This applies particularly to the current Covid 19 pandemic. Even those who only rely on reputable, scientific sources can easily lose track of the confusion of numbers and terms. A guide through the terminology of epidemiology.

infection

When scientists followed the beginnings of the Covid-19 epidemic, they were able to draw a conclusion quite quickly: Every person infected with the Sars-CoV-2 virus infects about two to three other people on average. This size is called Basic reproduction number R0.

If R0 is greater than one, the pathogen will spread more and more. If the number is exactly one, the number of infected people will remain constant over the course of the epidemic. The outbreak only subsides when R0 is less than one. The aim of all measures in the fight against the pandemic is to push R0 below one. At the moment this is mainly done by trying to limit contacts between people, so that the average sick person doesn’t even have the chance to meet two or three new victims.

In the longer term, this also happens on its own, provided that people are immune after an illness and the proportion of immune systems in the population increases (although this is not yet entirely clear in the case of Covid-19). Then the virus finds fewer and fewer people in whose bodies it can reproduce, and the new infections decrease. A simple formula shows how big this so-called Herd immunity must be in the population and thus the contagions decrease: R0 minus 1 / R0. For Covid-19, this means that the outbreak will only subside on its own if at least between 50 and 66 percent of all people are infected. Herd immunity can also be achieved by vaccination if there is a vaccine. It continues as long as no unprotected people come into the population through births or immigration.

From the outbreak to the pandemic

Of a outbreak speak scientists when suddenly more people have an illness than one would expect on average. This can happen when a known condition increases – or when a new illness occurs. In the latter case the expected value is 0 because there have never been any cases; Strictly speaking, a single patient is already an outbreak. In practice, an outbreak is often only recognized when there are already several patients. The label epidemic is scientifically synonymous with outbreak. However, since the term is generally associated with a certain drama, many scientists only use it for larger outbreaks.

If the epidemic extends to several continents, one speaks of one Pandemic. However, there is no general definition of how many continents have to be affected and how much. It used to be a strong warning signal when the World Health Organization officially declared the pandemic. In the meantime, the WHO has introduced a new regulation. Now she calls the Health emergency of international scope out. This is possible for all outbreaks regardless of their extent. When the WHO finally declared Covid-19 a pandemic, it meant little more than the recognition of reality: within two months, the virus spread across the globe.

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