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Can the virus come back? | Bernese Oberland

Are patients really permanently immune after surviving illness? There are signs of hope.

Specialists and imprisoned people ask themselves: when will the virus be successfully combated?

Photo: KEYSTONE

Will the victory last? More than half a billion people already carry the new corona virus within them, and a quarter of the world’s population is affected by isolation measures to slow the spread of the pandemic. Therefore, experts like those locked up ask themselves: Can the virus come back? Or are the people who have once been infected with Sars-CoV-2 and successfully fought it at least immune to it?

Nobody can answer this question at the moment. But there is hope that the victory over Sars-CoV-2 is an ongoing victory. When people have been through an infectious disease, they are mostly immune to the disease, often for the rest of their lives. This applies to measles, polio and rubella as well as to many colds.

«Virus has only undergone very few mutations»

The problem that humanity has with some viruses is their great variability. Influenza viruses appear every winter in a dress that is beyond recognition, the AIDS virus HIV changes so quickly that ultimately every person carries their own virus. In comparison, the new Sars-CoV-2 seems to be a guarantor of stability – even if one can hardly imagine that given its massive impact. “The virus has only undergone very few mutations on its way around the world,” says virologist Georg Bornkamm.


Bornkamm compared the genetic makeup of various Sars CoV-2 viruses. They come from patients from all over the world and were shared by scientists on the Gisaid platform. Accordingly, Sars-CoV-2 has changed only about ten places in its genome, even after its long journey from China to the United States, as molecular geneticist Peter Thielen from Johns Hopkins University told the Washington Post. “It’s a relatively small number of mutations that the virus has passed through such a large number of people.”

That’s good news. The stability of the virus gives rise to hope that a vaccine against Sars-CoV-2, if developed, will be effective for generations. This has long been the case for vaccines against measles, whooping cough and rubella, while a new vaccine is needed every year for the influenza virus.

If Sars-CoV-2 is so stable, it means something good: The virus will in all likelihood not have a second chance of multiplication in the body of people who have had an encounter with it before. The immune system builds very stable, durable weapons with its antibodies against pathogens it fights. These antibodies and their specialized production facilities, the B cells, are already there if the virus tries to attack the same person a second time. They attack the virus before it can multiply significantly.

The strange reports from China

A small study by Chinese scientists on rhesus monkeys suggests that this is not just gray theory. The researchers infected four animals with Sars-CoV-2 and re-infected them four weeks after their recovery. The animals were immune: they neither became sick nor found viruses in their blood. Since the immunology of rhesus monkey and humans is very similar, this could also apply to humans. It would have huge advantages: healthy people could go back to work, care for the sick and work in exposed jobs, because they themselves would not be contagious or at risk. However, every person’s immune defense is different, not all infected people produce equally strong immune responses with highly potent antibodies. It is possible that those who did not mind the infection and who survived without symptoms would not respond particularly well. All of this still needs to be clarified.

In view of all these findings, reports from China and Japan seem somewhat strange that some people may have been infected a second time. But Western scientists attribute this to faulty tests. In the meantime, the patients may not have been virus-free at all: The detection of the virus by means of PCR repeatedly incorrectly produces negative results, says corona expert Christian Drosten from the Berlin Charité. And Florian Krammer from Mount Sinai Hospital in New York points out that the test does not detect the virus itself, but only its genome. This means that he can again produce positive results for those who have recovered because the genome is sometimes still there when the virus has long been successfully combated.

Heal the critically ill with sera from survivors

However, it remains unclear how long the antibodies against the novel coronaviruses will remain. Could Sars-CoV-2 possibly frighten humanity again in a few years? “We still don’t know how long immunity will last,” says Isabella Eckerle, director of the Center for Viral Diseases at the University of Geneva. Only the experience with the closest relative of Sars-CoV-2 provides clues. Antibodies against the Sars-CoV-1 virus, which led to the Sars outbreak at the beginning of the millennium, are still found in the blood of once infected people after three to five years. “So the periods are rather years; it is not the case that you can become infected again with the exact same virus after a few weeks, »says Eckerle.

Thus, even if the laboratories are still, feverishly working on the development of vaccines against Covid-19, there may already be the first vaccines, namely in the blood of those who have recovered. Because with their antibodies other people could possibly be vaccinated. Such a “passive immunization” is somewhat “old-fashioned”, as Florian Krammer emphasizes. It was used in the early days of immunology, for example in the Korean War, to protect US soldiers from the Hantaan virus. But it is an approach. In unknown situations, old strategies are sometimes amazingly helpful. In any case, last Tuesday the US drug agency FDA started such an old-fashioned experiment: the first seriously ill people received serums from survivors.

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