Corona infection: not automatically immune?
According to the Federal Center for Health Education (BZgA), studies have shown that people who have had SARS-CoV-2 infection develop specific antibodies. "However, it is still unclear how robust and permanent this immune status will be and whether there may be differences from person to person," wrote the BZgA a few weeks ago. There are now more insights into this.
In many people shortly after being infected with the SARS-CoV-2 coronavirus, tests no longer find any special antibodies in the blood. What does that mean for herd immunity, immunity passports and the development of vaccines?
No antibodies detectable
In the corona pandemic, many people hope for immunity - after surviving infection or through a vaccination that will soon be available. Both of these could arm the immune system against the pathogen and protect people against the disease COVID-19. Now, however, many studies indicate that, especially in people who have had little or no symptoms, antibodies in the blood are no longer detectable soon after an infection.
Understanding of immunity unclear
It is still unclear what that means for a possible immunity. However, the observations raise doubts about the validity of antibody tests and the immunity passports currently under discussion. A precise understanding of the immune response to SARS-CoV-2 would also be crucial for the development of a vaccine.
The immune response appears to be inconsistent in humans. In principle, the immune system can react to pathogens with so-called T cells. Some T cells activate B cells, which then produce antibodies. Antibodies bind to certain characteristics of pathogens and can inactivate them.
At first glance, the presence of special antibodies seems to be a good indicator of an earlier infection. However, an investigation by the University Hospital Zurich found no so-called IgG antibodies in the blood of people with mild or asymptomatic courses. These are important for the immune memory - so that the immune system reacts stronger and faster when it comes into contact with the pathogen again.
So far, the study is only a preprint - it has therefore not been reviewed by experts or published in a specialist journal.
Researchers are unsettled
Another study published by the Lübeck Health Office as a preprint found no antibodies in 30 percent of 110 corona infected people who also had moderate COVID-19 symptoms. And in the journal "Nature Medicine", researchers from China report that the antibody concentration in the blood dropped significantly after a short time in infected people without symptoms.
Such studies make the validity of antibody mass tests, which should clarify the extent of the corona infection wave in the population, appear questionable. In addition, immunity given by antibodies in many SARS-CoV-2-infected people could disappear after a short time.
Accordingly, Thomas Jacobs from the Bernhard Nocht Institute for Tropical Medicine (BNITM) in Hamburg sees the introduction of immunity passports for people who have been infected with SARS-CoV-2. In any case, there is no scientific guarantee that the presence of antibodies automatically protects against renewed infection.
"We generally do not yet know exactly how antibodies protect," says the immunologist. Studies would suggest such protection, "but it remains unclear how high the antibody level must be, for example."
Antibodies have different qualities
Klaus Cichutek, President of the Paul Ehrlich Institute (PEI), emphasizes that one has to differentiate between antibodies: "There are different qualities of antibodies and not all prevent infection." It is important here to find hard data: "Whether one Immune protection arises, must be measured against reality. "
Likewise, Jacobs is not surprised by the results of the study that, in the case of asymptomatic illnesses, few or no antibodies can be found quickly: “A few viruses in the neck and throat area are probably not enough to trigger a large antibody response or T cell immunity.”
This adapted reaction makes sense for the immune system, since we are constantly exposed to pathogens in everyday life: "If we can answer with light weapons, we do not need to use heavy artillery." However, COVID-19 diseases with more severe symptoms will probably be a problem longer-term protection established.
Immunity remains only a few months
Studies on other coronaviruses indicate that renewed SARS-CoV-2 infection may prevent immunity from persisting for only a few months, as the virologist Shane Crotty from the La Jolla Institute of Immunology in California told Nature magazine. A symptom-relieving immunity could therefore last longer.
It is uncertain which part of the immune system is particularly important for this protection. "In addition to the antibody-producing B cells, the T cell response to the pathogen can be just as important," explains Jacobs. Which mechanism works above all is a central question for the development of a vaccine.
The infection researcher refers to studies from the USA and Germany: In it, up to 30 percent of people who were not infected with SARS-CoV-2 still had certain T helper cells that reacted to this coronavirus: “They have probably had it before Contact with so-called common cold corona viruses ”- in other words with other corona viruses that trigger conventional colds.
Such contact could offer partial immunity to COVID-19. "That would explain why there are so different dynamics and symptoms to be observed in the infection," presumes Jacobs. However, it is still unclear whether and what protection this so-called T cell reactivity could offer. (ad; source: dpa)
Author and source information
This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.
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