Anyone who carried the new Sars-CoV-2 coronavirus should be immune afterwards. Is that really true – and how reliable does this immunity hold?
By Franziska Meister
There is still no vaccination: The blue cell is infected with red Sars-CoV-2 virus particles (image taken with a scanning electron microscope). Photo: Handout, NIAID / National Institutes of Health, Keystone
They are the new shooting stars among the scientific experts: virologists such as Christian Drosten from the Berlin Charité, who explains and classifies various aspects of the corona pandemic in a daily podcast by Norddeutscher Rundfunk. A few days ago, he reported an animal experiment from China in which four rhesus monkeys were infected with Sars-CoV-2, only to have three of them fully recovered before they were infected again. None of the three fell ill again. An ethically problematic investigation – but with a result that gives hope: Does it also apply to people that they are immune after being infected with Sars-CoV-2? And is this immunity permanent?
Benjamin Meyer, virologist at the University of Geneva, deals with questions like these. “With the already known corona viruses, we know that immunity lasts for about two years,” he says. “Afterwards, it is basically possible to become infected again, although such a secondary infection is probably usually much milder.” Does this also apply to the new Sars-CoV-2 coronavirus? After all, China has reported people who have been infected a second time.
Meyer points out that it is not clear from these reports how high the viral load was when the tests were again positive. The commonly used test identifies throat genetic virus material. The virus can still be found there weeks after infection. Because the viral load decreases over time after an illness, the reliability of this test also decreases. Depending on the location in the throat where the smear is taken, viruses are still present or no longer. “That is why someone who has tested negative at first can be tested positive again a few days later,” Meyer says, adding with reference to the cases from China: “It does not have to mean that the person takes a second test Infected. »
Special antibodies
Basically, Sars-CoV-2 can be detected in two ways. The throat swab is a so-called antigen test – it identifies the virus directly. In the antibody test, the virus is detected indirectly via antibodies in the blood. These are formed in response to viruses. In the case of Sars-CoV-2, our body only produces such an immune response after seven to twelve days. An antibody test is therefore unsuitable for early identification of infected people. However, it is important for epidemiological studies that examine the proportion of people in a population who have already had an infection and are immune.
However, antibodies alone do not guarantee immunity – they recognize the virus but cannot prevent it from penetrating the cells and causing inflammation there. In order to actually switch off a virus, a specialized form of antibodies must be activated, so-called neutralizing antibodies. They can be detected in the blood serum for up to ten years after an infection, whereby their number and thus the immunity decrease over time.
In the case of Sars-CoV-2, not all infected apparently form such neutralizing antibodies. At least Drosten reports of several cases among the early Covid-19 sufferers from Munich who had no neutralizing antibodies in their blood after their recovery. He suspects that they got well again because other immune reactions, such as in the cellular immune system, were fighting the virus. Meyer, too, is likely to make them immune to Sars-CoV-2. “However, long-term studies have to show more details.”
For sustainable vaccination protection
Neutralizing antibodies play a key role in the development of vaccines. Various biotech companies are currently trying to isolate them from blood donations from people who have recovered from Covid 19 and use them to produce so-called mono- or polyclonal antibodies. This would enable passive immunization. However, this lasts only a few weeks and at best means that an infected person does not get sick as quickly and violently – Drosten and Meyer are both rather skeptical.
Sustainable vaccination protection requires active immunization, in which the immune system is provoked to produce as many neutralizing antibodies as possible. This can only be achieved with a vaccine that contains the virus in a modified form: either as a still active virus that multiplies in the body – such as measles – or in the form of individual proteins of the virus that are not capable of reproducing themselves. An example of this is the seasonal flu shot. In their case, the vaccine has to be readjusted every year because influenza viruses quickly mutate and change their properties.
Corona viruses also mutate. “Despite these mutations, they are relatively stable,” says Benjamin Meyer. “One of the vaccines that will be available should therefore be able to neutralize the Sars-CoV-2 in the long term – provided its quality is high.”
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