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The report by South Korean authorities caused a sensation on Friday. 91 people who had already recovered and had been released from quarantine were again tested positive for the new coronavirus. The Korean Center for Disease Control (KCDC) believes that these are not new infections. The virus is more likely to have “reactivated,” said KCDC chief Joeng Eun Kyeong. South Korean virologist Kim Woo Joo anticipated a further increase in “reactivated” coronavirus cases: “91 is just the beginning.” South Korean authorities and the World Health Organization (WHO) immediately announced new investigations.
Until now, the phenomenon has been little investigated, but not new: as early as February, four doctors in China detected the virus and survived Covid-19 and tested negative twice. 172 patients were examined in the Chinese metropolis of Shenzhen. In 25 of them, the PCR test was positive approximately one week after the last negative result. In Wuhan, doctors found five recently positive cases among 55 recovered people; in four of them, those affected had even developed mild symptoms, such as fever, cough and sore throat, the “Zeit” reported.
There are many signs of immunity.
The question of whether people recovering from infection can re-become infected with the coronavirus is of international importance. Many countries believe that people recovering from a CoV infection develop immunity to the virus, and that over time a large enough part of the population is immune to the disease to prevent the pandemic from reoccurring, keyword immunity collective.
Initial studies indicate that the majority of recovered CoV-infected have generated sufficient antibodies against the virus. The head of the US Institute of Infectious Diseases and Allergies. USA, Anthony Fauci, assumes that immunity to SARS-CoV-2 is at least months. Studies after the first SARS pandemic in the early 2000s, which was also caused by a coronavirus, also provide evidence of this. Studies have reported stable immune responses in survivors of the disease two years after infection.
“Vaccination failure” and incorrect test results
However, in some people, the immune system produces enough antibodies to fight the disease, but not enough for long-term immunity. That is “not unusual,” said Viennese pulmonologist Gernot Rainer of the “Press”: “For example, there are also people, often children, who do not form enough antibodies after a vaccine to be protected, so-called vaccination failures “
In these cases, the virus can actually “reactivate” under certain conditions. There are also viruses that can rest in the body for years, such as HIV or the varicella zoster virus from the group of herpes viruses. It causes chickenpox in childhood and shingles in adulthood. From a scientific point of view, it would be new from a scientific point of view if a corona virus also fell asleep for years, Die Zeit wrote.
However, the phenomenon observed in South Korea and China could also have a much more banal reason: incorrect test results. Direct detection of the virus is carried out with PCR (polymerase chain reaction) tests, which are considered extremely reliable. However, stain errors can occur. According to Chinese experts, the sampling time is also important, since the concentration of the virus in the nose and throat can change in the course of the disease.
No risk of infection despite virus detection.
Some CoV positives excrete the virus in small amounts long after the disease has disappeared, as studies show. However, this does not automatically mean that those affected present a risk of infection. “If there is an infectious virus, one person can infect another. However, the virus load for many viruses has to be high, “said Florian Krammer, a vaccination professor at the Icahn School of Medicine in New York.
“But what is detected with the PCR test is not the virus, but the genome of the virus. And it often happens that the virus genome is still present, but it is no longer an infectious virus. This is usually the case with measles for months, “says Krammer.
The worst case scenario: the mutation
Pulmonologist Rainer also brought the worst-case scenario for the “press” into play: a powerful mutation of SARS-CoV-2. This scenario would be absolutely fatal not only for the development of a vaccine. “Confirmation of a virus mutation and associated new infections would render the concept of collective immunity obsolete once and for all and catapult us early in our fight against the virus,” said Rainer.
However, there is currently little evidence that this “worst case” has already occurred. In a study published these days, bioinformatics Niema Moshiri and her team at the University of California, San Diego looked more closely at the genetic material of the pathogen. Result: SARS-CoV-2 mutates, but apparently much more slowly than influenza viruses. The SARS-CoV-2 genome is twice as large as that of influenza viruses, making the latter appear to mutate four times faster, Moshiri wrote. That gives hope in the development of an effective long-term vaccine.
