Does Covid 19 infection automatically lead to immunity?

Current studies show that many people have no special antibodies in their blood shortly after a corona infection. What does that mean for immunity?

Many people are hoping for the corona pandemic immunity – after surviving infection or through a vaccination soon available. It could do both immune system arm against the pathogen and people from the disease Covid-19 protect.

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 would also be necessary for the development of a vaccine SARS-CoV-2 central.

The immune response appears to be inconsistent in humans. Basically, the immune system can use so-called T cells react to pathogens. Some T cells activate B cells, which then form 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 in 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.

Investigations of the antibodies unsettle researchers

Another study published as a preprint by the Lübeck Health Office found no antibodies in 30 percent of 110 corona patients with likewise 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 how high the antibody level must be, for example, remains unclear”.

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 to find hard data here: “Whether immune protection is created must be measured against reality.”

Likewise, Jacobs is not surprised by the results of the study that especially with asymptomatic illnesses, few or no antibodies can be found quickly: “Few Viruses in the neck and throat area is probably not enough to have a large antibody response or T cell immunity trigger. “

This adapted reaction makes sense for the immune system, since we are constantly exposed to pathogens in everyday life: “If we can respond with light weapons, we do not need to use heavy guns.” In the case of Covid 19 diseases with more severe symptoms, however, long-term protection is likely to be built up.

Immunity remains only a few months

Studies on other coronaviruses indicate that renewed SARS-CoV-2 infections may prevent immunity from remaining completely for only a few months, as the virologist Shane Crotty from the La Jolla Institute of Immunology in California told the journal “Nature”. A symptom-reducing immunity could therefore exist 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 on the pathogen just as important, “explains Jacobs. Which mechanism works above all is a central question for the development of a vaccine.

Partial immunity to Covid-19 without infection?

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, the on this Coronavirus responded: “They have probably already had 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 in the infection,” Jacobs suspects. However, it is still unclear whether and what protection this so-called T cell reactivity could offer.

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