Coronavirus in recovered people: search for explanations

The report by the South Korean authorities caused a sensation on Friday. 91 people who were already recovered and had been released from quarantine were again tested positive for the novel corona virus. The Korean Center for Disease Control (KCDC) believes that these are not new infections. It is more likely that the virus has “reactivated”, said KCDC boss Joeng Eun Kyeong. South Korean virologist Kim Woo Joo anticipated a further increase in “reactivated” coronavirus cases: “91 is only the beginning.” South Korea’s authorities and the World Health Organization (WHO) immediately announced further investigations.

The phenomenon has so far been little researched, but not new: As early as February, the virus was detected by four doctors in China who had survived Covid-19 and had tested negative twice. 172 patients were examined in the Chinese metropolis of Shenzhen. In 25 of them, the PCR test was positive about a week after the last negative result. In Wuhan, physicians found five newly 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 an infection can become infected again 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 sufficiently large section of the population is immune to the disease to prevent the pandemic from flaring up again – keyword herd immunity.

Initial studies indicate that most of the recovered CoV infected have raised enough antibodies against the virus. The head of the US Institute for Infectious Diseases and Allergies, Anthony Fauci, assumes that immunity to SARS-CoV-2 is at least months. Evidence of this is also provided by studies after the first SARS pandemic in the early 2000s, which was also triggered by a corona virus. Studies have reported stable immune responses in survivors of the disease two years after infection.

“Vaccination failure” and wrong 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 “nothing unusual,” said Viennese pulmonologist Gernot Rainer of the “Press”: “For example, there are also people, often children who do not form sufficient antibodies after a vaccination 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 that a corona virus would also go into sleep for years, wrote Die Zeit.

However, the phenomenon observed in South Korea and China could also have a much more banal reason: incorrect test results. The direct virus detection is carried out with PCR tests (polymerase chain reaction), which are considered to be extremely reliable. However, mistakes can happen in the smears. According to Chinese experts, the time of sampling is also important, as the virus concentration 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 subsided, as studies show. However, this does not automatically mean that those affected pose 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, professor of vaccinology at the Icahn School of Medicine in New York.

“But what is detected with the PCR test is not the virus, but the virus genome. And it often happens that the virus genome is still present, but no longer an infectious virus. This is often the case with measles for months, ”says Krammer.

The worst case – the mutation

Pulmonologist Rainer also brought the absolutely worst case into play for the “press” – a far-reaching mutation of SARS-CoV-2. This scenario would be absolutely fatal not only for the development of a vaccine. “The confirmation of a mutation of the virus and the resulting new infections would make the concept of herd immunity obsolete once and for all and catapult us back to the start of 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, bioinformatician Niema Moshiri and his team from the University of California in San Diego took a closer look at the genetic material of the pathogen. Result: SARS-CoV-2 mutates, but apparently much more slowly than flu viruses. The genome of SARS-CoV-2 is twice the size of that of influenza viruses, so the latter seem to mutate four times faster, wrote Moshiri. That gives hope in the development of a long-term effective vaccine.

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