SProtective antibodies against the coronavirus are often not detectable in the blood of previously infected people after a while. This is shown by further study data. The Robert Koch Institute collected them between November 17 and December 5, 2020 at the beginning of the second wave of infections in the then highly polluted district of Berlin-Mitte and has now evaluated them. Accordingly, around half (48 percent) of the adults who said they had tested positive for SARS-CoV-2 before the start of the study had no so-called neutralizing antibodies.
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. The result speaks once more for a vaccination, said RKI President Lothar Wieler on Wednesday. With cororaviruses it is generally not atypical that the antibody protection expires faster than with other viruses.
With the study, the RKI also wanted to gather information on the number of unreported infections. Around 2,200 adults in the Berlin-Mitte district, who were written to representatively, took part in the study. They were ready for a throat swab and blood sample. The smear was for an acute infection. Antibodies that can keep the virus in check (neutralizing antibodies) can also be determined from blood samples.
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 the time indicated. In the case of the diffuse outbreak, as it was then in 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 5 percent of the participants were acutely infected or had already gone through an infection.