Medical officials in South Korea are investigating several possibilities to explain the increasing number of patients who have recovered from Covid-19 only to later test positive for the coronavirus.
South Korea has already reported less than thirty new cases of the disease for four days in a row, but cases of the "return" of the virus are causing great concern to experts.
According to experts, the main possible explanations are re-infection, the return of the virus or unreliable tests.
According to yesterday's data, 141 such cases were recorded in South Korea, the Center for Disease Prevention and Control (KCDC) said.
Half of these patients again have symptoms of covid-19, while the rest are positive but asymptomatic. A quarter of them are young people in their twenties.
"In cases of other coronaviruses such as SARS and MERS, it did not happen that people tested positive after full recovery, said Kwon Jun-wook, deputy director of the KCDC.
"This new coronavirus is very evil and insidious." He said that it will take about ten days or two weeks for the health authorities to analyze these cases, since they have to check a series of information, including the production of antibodies.
New infection and virus reactivation?
Although re-infection would be the scenario that causes the most concern because it would have catastrophic consequences for the development of immunity in the population, experts say that this is unlikely.
Instead, the Centers for Disease Control and Prevention claim that they are more inclined to the option that it is a return or "reactivation" of the virus.
This means that parts of the virus are "dormant" for a while, or that some patients have certain conditions or weak immunity that makes them susceptible to reviving the virus in their system, according to experts.
A recent study conducted by doctors in China and the United States has shown that the new coronavirus can damage T lymphocytes, also known as T cells, which play a key role in the human body's immune system and its ability to fight infections.
Kim Jeong-ki, a virologist at Korea University's School of Pharmacy, compared the reactivation of the virus after treatment to a stream of water coming back after you blocked its path with your hand.
"When you press the jet, it becomes smaller, but when you take your hands away, it comes out again," he told Reuters.
Even if it is established that the virus has reactivated, and not that there has been a new infection, it foreshadows new challenges in suppressing the spread of the epidemic.
"South Korean medical authorities have not yet discovered cases in which "reactivated" patients spread the virus to a third person, but if such infections are recorded, then it would be a huge problem," said Seol Dai-woo, an expert on vaccine development and professor at Chung-Ang University.
Inaccuracy of tests
Patients in South Korea are considered clear of the virus when they test negative twice within 48 hours.
Although the RT-PCR tests used in South Korea are generally considered accurate, experts say there is a way for them to give false or inconsistent results in a small number of cases.
"RT-PCR tests are supposedly accurate in 95 percent of cases. This means that there may still be those 2-5 percent of cases that show a false negative or false positive result," said Kim.
Remnants of the virus may be at too low a level for this test to detect, Seol said.
On the other hand, the tests can also be so sensitive if they pick up a small, potentially harmless amount of the virus, leading to new positive results even though the person has recovered, Kwon told Reuters.
Tests can also be compromised if necessary samples are not taken properly, said Eom Junk-sik, a professor of infectious diseases at Gachon University.
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