No more antibodies: does the immune system still react?
The coronavirus poses major challenges for the human immune system. Antibodies in particular, which are formed after an infection or vaccination, play a crucial role. But how does the immune system react when the antibody level decreases or is no longer available? This is how our body protects itself from SARS-CoV-2 and that is why a booster vaccination is particularly important.
Anyone who no longer has antibodies against the corona  virus due to the time difference is still not completely at the mercy of the virus. Other antibodies also fight the pathogens.
This is how the body defends itself against SARS-CoV-2
Anyone who has already been infected with SARS-CoV-2  or is fully vaccinated forms a strong immune response against the coronavirus. Such is the reaction of the immune system to unknown or already known foreign bodies. Various antibodies are involved in the immune response. The following antibodies are particularly important in the fight against SARS-CoV-2.
Antibodies neutralize viruses
Antibodies, so-called immunoglobulins , are formed after an infection or vaccination and neutralize the respective pathogen in the human body if an infection occurs again. They remember the structure of SARS-CoV-2, recognize the spike protein of the virus and thus prevent it from docking with human cells. The antibodies are mainly immunoglobulin G (IgG) antibodies, which form the main defenses in the blood.
 There is also IgA, which is responsible for the defense, especially in the saliva . IgM, in turn, is responsible for the primary immune response that takes place as soon as a pathogen enters the body for the first time.
B cells responsible for producing antibodies
B cells belong to the white blood cells . After contact with unknown viruses or bacteria, they begin to produce antibodies against the pathogens in order to be able to prevent reinfection if they come into contact again.
T cells recognize infected cells
T cells intervene when the virus has evaded the antibodies and infects human cells. They recognize the affected body cells and kill them to prevent the virus from spreading in the body. In addition, T cells can also activate B cells to produce antibodies.
Vaccination and infection provide a specific immune response
T cells and B cells are part of what is known as the specific or adaptive immune system. Their advantage is the great adaptability to new or modified pathogens such as SARS-CoV-2. The adaptive immune response is acquired throughout life through infection or vaccination. After contact, the body retains pathogens in its immunological memory and can therefore react more quickly. This means that even if there are no longer any antibodies against SARS-CoV-2 in the body, the adaptive immune system  remembers the pathogens and can produce antibodies again in the event of an infection.
Study shows: This is how important B cells and T cells are against omicron
Studies show that higher antibody levels are an important, but not the only, factor in protecting vaccinated and recovered individuals.
Researchers led by Edgar Meinl at the Biomedical Center of the University of Munich analyzed the blood of 17 unvaccinated corona infected people. There is a high probability that the participants became infected with the wild type of SARS-CoV-2 in 2020, but no more IgG antibodies could be detected in the blood.
However, the experts were able to detect B cells in the blood that were able to produce antibodies against SARS-CoV-2. In 13 people, the infection was at least five months ago, in others eight months had already passed.
B cells can “be mobilized in just a few days,” as Edgar Meinl explained to Deutsches Ärzteblatt. Together, B-cells and T-cells can induce a rapid immune response, thus reacting specifically to virus variants and preventing severe courses.
Response of the T-cells at omicron: booster vaccination recommended
A previously published study from the USA examined the T-cell response of 76 vaccinated or recovered patients.
The participants were
- unvaccinated but recovered
- double vaccinated
- or already boosted.
The samples were taken on average about 220 days after the primary vaccination or eight to 54 days after the booster vaccination.
The T cell response against the omicron variant persisted in a majority of infected and vaccinated individuals. In 21 percent, however, only low activity (less than 50 percent) against omicron could be detected. A booster vaccination is recommended because the T-cells may be less able to recognize the omicron after a while. According to the results, a third vaccination resulted in a 20-fold response in most participants.
Experts from science and politics continue to analyze in detail how long those who have been vaccinated and those who have recovered are protected from renewed infection and whether further vaccinations make sense.