Antibody tests – how useful are they?

With the number of new infections, the fear of a breakthrough infection increases in many people. Some are therefore already waiting for the recommendation of a refresher, others are carrying out antibody tests in the general practitioner’s practice. But what does the procedure say about the immune response?

 After an infection or vaccination has been overcome,  the  immune system produces antibodies against certain pathogens – this is also the case with SARS-CoV-2 . The immune response against COVID-19 is particularly directed against the spike protein, which allows the virus to dock to human cells. These antibodies can be determined using a special test.

What does an antibody test really say?

Many people have their antibodies tested to find out whether and how well the vaccination worked. Although the antibody test could provide initial statements about the effectiveness of the vaccine, doctors are currently finding it difficult to adequately assess and assess the procedure. Several factors are responsible for this:

  • Insufficient limit values:  Although antibody tests can determine the number of antibodies, the limit values ​​for an effective vaccination are not yet known. Several teams of experts are already trying to establish a limit value, also known as an immune correlate, based on the first series of tests. Due to the small number of participants and only a few published studies, however, no generally valid immune correlate has yet been defined.
  • Virus variants:  Different virus mutations make it increasingly difficult to determine the effectiveness of the vaccine. While vaccines provide good protection against infection with the original type, their effectiveness against the aggressive delta variants is sometimes greatly reduced. Not all antibodies recognize the virus quickly and reliably, and the protection afforded by the vaccination decreases. For example, initial studies show that the effectiveness of the BioNTech/Pfizer vaccine could decrease after six to nine months.
  • T cells:  In addition to antibodies, the T cells of the immune system also play an important role in fighting diseases. T helper cells support the immune system in a different way. If the virus is already in the cell, the antibodies can no longer reach it. T cells recognize the infected cells and help to destroy the infected structures. In this way, the spread of the virus in the body can be stopped.

Is an antibody test necessary before the booster vaccination?

The common assumption that a booster vaccination is not required if the antibody level is high cannot be confirmed.

The Standing Vaccination Commission (STIKO) is currently recommending the booster vaccination for certain groups of people. Anyone who falls into this risk group should take advantage of the booster vaccination without having to carry out an antibody test beforehand.

If this is nevertheless considered by the doctor, the test can certainly be rejected. It must also be taken into account that the costs of an antibody test – unless there is a direct temporal connection to COVID-19 symptoms – must be borne by yourself.

The doctor in charge must carry out the booster vaccination without an antibody test at the patient’s request and according to the recommendation of the STIKO.

Figures from Israel, where booster vaccinations have been carried out since the summer, show that the situation has calmed down despite an increasing incidence and that a booster vaccination is recommended for risk groups.

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