The KCDCs analyzed 285 cases of COVID-19 convalescent individuals, who were then again tested positive for coronavirus through a swab test, which is based on the analysis of saliva and mucus in search of fragments of the genetic code (RNA) of the coronavirus. As appropriate, the patients had tested positive for the virus again one to 37 days after their recovery and the end of their isolation period. On average, the time span of the new positivity was around two weeks.
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The researchers then analyzed the patients’ medical history, noting that about half had experienced new symptoms attributable to coronavirus, albeit in milder forms than in the first phase of the disease. None of them, however, had become contagious again, at least based on the information collected by tracking the people with whom they had come into contact.
For 108 patients, other laboratory tests were then performed to check if they were still contagious. Analyzes showed that none of them had coronavirus forms still active and therefore able to transmit to other people.
To date, swab testing is the best tool for detecting the presence of coronavirus in an individual at any given moment: it allows you to identify the virus RNA and therefore the degree of infection. In recent months, however, it has become evident that in some cases a positive outcome does not necessarily indicate that the infection is still active and that the viral particles (virions) coming from the person examined are able to infect other individuals. The test in fact detects the presence of the coronavirus genetic material, which could be in deteriorated and no longer dangerous forms.
According to KCDC research, this should be the case for patients analyzed and who tested positive for coronavirus again. They concluded it after trying to isolate and cultivate the virus from the samples taken, noting that they had not obtained active versions.
The researchers then performed a blood test on 23 newly positive patients, detecting the presence of neutralizing antibodies to coronavirus in 96% of cases. To date, it is not yet clear whether one becomes immune and for how long, but the presence of these antibodies and the lack of significant relapses among the patients studied seems to suggest that the organism keeps a memory of the infection, managing to counter it.
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The study released by the KCDC is still preliminary and is based on a relatively low number of patients, but it offers important new clues to better understand why some people recovered are still positive for coronavirus. The South Korean health authorities believe that much derives from the sensitivity of the tests through the swab and that therefore the “again positive” are actually “returned positive”, therefore without having suffered a second infection.
In recent months in many countries, including Italy, cases of patients recovered from COVID-19 have been reported and positive results weeks later. As reported also by the experts of the Istituto Superiore di Sanità, it is probable that in most cases these people have kept some traces of the coronavirus, in a form that is no longer active, but still detectable through tests.
This circumstance seems to rule out the possibility that the coronavirus can be contracted a second time after falling ill, at least in a short time. Not knowing, however, whether and however much you remain immune from the virus, it will still take months and new research to fully understand the mechanisms that lead to possible immunization and its maintenance.