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Draw blood for the antibody test
Photo: Angelika Warmuth / dpa
Protective antibodies against the coronavirus are often not detectable in the blood of previously infected people after a while.
This is shown by new study data from the Robert Koch Institute (RKI).
The result speaks once again for a vaccination, said RKI President Lothar Wieler.
With cororaviruses it is generally not atypical that the antibody protection expires faster than with other viruses.
Between November 17 and December 5, 2020, the data from 2287 people were collected and evaluated in the then highly polluted district of Berlin-Mitte, which is considered a representative random sample.
They had to state in a questionnaire whether they had previously tested positive for Sars-CoV-2, take a throat swab and their blood was drawn.
Not only antibodies contribute to immunity
In around half (48 percent) of the adults who stated that they tested positive before the start of the study, no so-called neutralizing antibodies were detectable.
However, this does not necessarily mean that they have no immunity, the RKI and the district office in Mitte announced on Wednesday.
Because there are other protective mechanisms in the body, such as memory T cells.
With the study, the RKI also wanted to collect findings on the number of unreported infections.
As a result, 21 acute Sars-CoV-2 infections were detected during the investigation.
That corresponded to around one percent of all study participants.
For the authors, the figure shows that the number of infections was slightly under-recorded at this point in time: the study detected 2.2 times more acute infections than the official reporting figures at that time.
In the case of the diffuse outbreak, as it was then in Berlin-Mitte, this value of a possible dark figure is not high.
Antibodies as proof of a previous infection could generally be detected in 4.4 percent of the participants, but neutralizing antibodies against Sars-CoV-2 were only detected in 2.4 percent.
Overall, the study shows that around five percent of the participants were acutely infected or had already gone through an infection.
The RKI's "Corona Monitoring Local" study is running in four municipalities across Germany.
The institute wants to collect findings on immunity, the number of unreported cases and the symptoms of Sars-CoV-2 at individual particularly affected locations.
Monitoring was still carried out in Bad Feilnbach, Kupferzell and Straubing.
There, too, it was found that many corona positives no longer have neutralizing antibodies.
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