Coronavirus: immune after infection?

Florian Tiefenböck studied human medicine at the LMU Munich. In March 2014, he joined as a student and has supported the editorial team with medical articles ever since. After receiving his medical license and practical work in internal medicine at the University Hospital Augsburg, he has been a permanent member of the team since December 2019 and, among other things, ensures the medical quality of the tools.

More posts by Florian Tiefenböck All content is checked by medical journalists.

Scientists are researching the novel coronavirus Sars-CoV-2 at full speed. It has only been known for a few months - much is not yet known. It has not been proven that people are immune after surviving infection, but according to researchers it is likely.

Acquired immunity

According to experts, people who have survived an infection with Sars-CoV-2 are probably initially immune to the pathogen.As of today, we know that humans form antibodies after being infected with the novel coronavirus, explained virologist Melanie Brinkmann from the Helmholtz Center for Infection Research in Braunschweig and Friedemann Weber, head of the Institute for Virology at the University of Giessen.

The body uses these antibodies to fight intruders such as the novel coronavirus. Once the infection has passed through, the immune system “remembers” the pathogen. If a person is then infected again with the same germ, the body can fight it off faster - and does not get sick. Physicians call this adaptive or acquired immunity. How long it lasts varies from pathogen to pathogen.

According to the Berlin virologist Christian Drosten, it takes about ten days for antibodies to form after an infection with the coronavirus. Antibodies that are still present from this first infection protect above all from a new disease if the person is infected again with the pathogen shortly afterwards.

Experience with other coronaviruses

It can be assumed that the immune protection will last one to two years after infection. This assumption is based on experience with other coronaviruses that people get sick with - usually with a cold. "In all likelihood, after being infected with the Sars-CoV-2 virus, you will be protected from renewed infection for at least a few years," said the President of the German Society for Immunology, Thomas Kamradt.

However, this cannot be said exactly yet, after all, antibody tests are only just coming out and long-term examinations are not yet possible, as the Covid-19 disease has only been known for a few months.

How long is it protected?

How long this protection lasts depends, according to Kamradt, on the rate at which the concentration of antibodies in the blood, the so-called antibody titer, decreases. The higher the titer, i.e. the number of antibodies, the stronger the protection. It would be "extremely unusual" that the antibodies produced in the body against the novel coronavirus do not protect against renewed infection.

According to the medical director of the Institute for Laboratory Medicine at Marienhospital Stuttgart, Matthias Orth, it is not yet possible to say with certainty whether the antibodies that are formed protect against renewed infection. It is still unknown at what concentration of antibodies there is protection and how often renewed infections occur.

Why do only some get seriously ill?

According to Brinkmann and Weber, it will also be interesting to examine the antibody titers of people with different disease courses. This could answer the question of whether people with severe disease had actually produced enough antibodies. The question of when specific antibodies are formed during the course of the infection could also be answered.

Cross immunity

It is also an exciting question whether previous infections with another coronavirus also protect against illness from the novel coronavirus Sars-CoV-2 - or at least partially mitigate the course of the disease.

Other coronaviruses that cause colds in humans have been known for a long time (Humane Coronaviridae = HCoV-NL63, -229E, -OC43, -HKU1). And we know from other illnesses that an infection with one type of pathogen can also protect against illness caused by a related type. For example, if a person has had cowpox, they are also immune to smallpox.

Determine the number of unreported cases

According to Brinkmann and Weber, it is now particularly important to carry out extensive tests with reliable antibody tests. This is important to determine the number of unreported cases: How many people have already gone through the infection without being noticed? How high is the population's basic immunity now?

According to statistical projections, around 60 to 70 percent of the population must have become infected before the pandemic wave comes to a standstill on its own - i.e. without a protective vaccination. Knowing about a previous infection is also important in order to give people with existing immune protection the “green light”, for example for work. (ft / dpa)

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