Antibodies form one of the body's most important defense reactions against viruses, bacteria or fungal infections. Especially in connection with the coronavirus and the resurgence of high Infection figures more people are currently interested in antibodies and other immune system processes than before the Pandemic. But what exactly do antibodies do, and at what point do they form sufficient protection against infection with SARS-CoV-2?
To do this, it is first worth taking a look at the Basic: Antibodies – also known as immunoglobins (Ig) – are proteins that the immune system uses to defend against pathogens. Through contact with antigens, such as viruses, the immune system can form suitable antibodies in each case. At the next contact, it then rebuilds the antibodies from its memory and can fight the infection. Vaccinations help with this immunization process. But especially in the context of corona virus, there are still many questions.
How many antibodies are needed?
Most vertebrates have five different classes of antibodies in them; they are largely found in the blood. The most important antibodies for the defense reaction are the immunoglobins A, M, G and E. The IgA is mainly located on mucous membranes, for example in the respiratory tract or in the gastrointestinal tract, and prevents the penetration of antigens there. The IgE is used to defend against parasites. It is also possible for the body to build antibodies against its own components and fight itself off. In such cases one speaks of an autoimmune disease.
How many antibodies It is not possible to give a general answer to the question of which antibodies one should carry. This is because, as a rule, only one type of antibody matches an antigen according to the lock-and-key principle. How many of these help against different pathogens and make the body immune is determined by different threshold values, which must first be determined on the basis of research.
However, for some pathogens there are large-scale vaccinations, to immunize as many people as possible: for example, against measles, mumps, rubella or even SARS-CoV-2. After appropriate research and long-term studies, authorities such as the Robert Koch Institute (RKI) then ame for such pathogens that immunity has been achieved after a certain vaccination sequence. In some cases the vaccination must be refreshed. After that, it is not absolutely necessary to check the antibody levels in the blood. In individual cases, however, the test can help to understand certain symptoms and diseases and, if necessary, to initiate therapeutic measures.
How many antibodies protect against Corona?
The most important antibodies to the Protection against Corona are the IgM, the IgA on the mucous membranes and the IgG. While the former are formed shortly after the first symptoms of Covid-19 as a reaction, the IgG with the help of the memory cells appear later – and remain longer. They are considered markers of immunity for SARS-CoV-2 as well as for many other viruses.
The maximum antibody titers – i.e., the amount needed to produce a biological response – vaccinated individuals usually achieve a high immune response two weeks after completing basic immunization against Covid-19. After that it decreases, as an analysis of the six-month data of the Biontech/Pfizer vaccine showed. However, it is not yet sufficiently clear how quickly and strongly the number of antibodies decreases and when the protection is no longer effective. In fact, researchers around the world are still trying to define the level at which one is considered protected against the coronavirus.
However, the body has other means of defending itself against viruses besides antibodies: Activated T lymphocytes (also called T cells) can eliminate virus-infected cells, preventing the virus from spreading further. It is possible that a person has a low antibody level against SARS-CoV-2 and still does not get seriously ill. However, it is very difficult to T cells to measure.
What does an antibody test cost?
For this reason Antibody tests as little meaningful to draw exact conclusions about an immunity against SARS-CoV-2. Those who have a high number of antibodies in their blood must therefore still adhere to the protective measures. The tests are especially helpful if antibodies against the coronavirus are to be detected in general, for example if a person has not yet been vaccinated and wants to know if he or she has already survived an infection. However, antibody tests can also be used to find out whether and how well the vaccination has worked.
Depending on the Test method, costs vary. Surrogate neutralization tests, in which the blood is brought into contact with viral elements and tested for their reaction, are more precise and more expensive than simple antibody tests at 50 to 60. In this case, the family doctor takes blood and sends it to the laboratory, the tests cost about 15 to 20 euros. In addition, if an antibody test has been prescribed by a doctor, some statutory health insurers will cover the costs.
No antibodies after vaccination, what to do??
Even if it is not clear at what antibody titer a person is immune to the coronavirus: those who have antibodies are in any case better protected against a severe course than someone who does not have any. But what if, even after vaccination against Covid-19 no antibodies have formed?
The Standing Commission on Vaccination (STIKO) has observed in studies that some people have a poorer immune response had. In an interview with "Tagesschau", STIKO chairman Thomas Mertens explained that this applies above all to people whose immune system is slowed down by medication. This includes, for example, persons with new donor organs or patients undergoing chemotherapy. Also, some people with autoimmune diseases can get medications that inhibit vaccine effectiveness. In addition, the immune system often reacts less reliably and stably with increasing age than in younger vaccinated persons.
In the 12. The STIKO is therefore advising affected groups of people to update the vaccination recommendation Vaccination boosters after six months. A previous antibody test, in order to be sure that the vaccination protection has actually decreased, is however not necessary in principle and also not helpful: The value, which determines the protection status, is not defined finally yet. Only "severely immunodeficient persons with an expected strongly reduced vaccination response" should have their antibodies tested again, advises the STIKO. And before and after the third vaccination dose.
How long are antibodies detectable?
Due to the fact that there is still very little data on the Long-term antibody level Although there is no clear evidence that there is a significant increase in antibody levels after the Covid 19 vaccination, this question also cannot yet be answered unequivocally. Researchers currently ame that it will relatively certainly have dropped significantly one year after vaccination. However, a booster vaccination is also considered safe if the antibody level would still be high at the time of its administration.
Quite different after survived infectionLast year, studies in the United Kingdom and China showed that antibody levels had already fallen sharply after two and three months, respectively. In general, it is therefore amed that there is no longer sufficient protection at the latest six months after the infection has been overcome.