People who test positive for Covid-19 for a second time after recovering from the disease appear to be incapable of transmitting the infection, suggests new data from South Korean health authorities.

South Korea, along with China and Japan, has documented a significant number of “re-positive” cases, where people who had recovered from Covid-19 test positive again for the virus days or weeks later. While there is still a lot of uncertainty surrounding re-positive cases, the new research does allay some fears that these people are still contagious and can spread the infection.

Scientists from the Korean Centers for Disease Control and Prevention (KCDC) studied 285 people across the country who tested positive for Covid-19, recovered from the sickness, then later tested positive again. They traced almost 800 people who were in contact with these re-positive patients and found no evidence they had been infected. Oddly, however, nearly 45 percent of re-positive cases still had Covid-19 symptoms, such as a dry cough. 

The KCDC tested re-positive cases using RT-PCR tests (reverse transcription-polymerase chain reaction), which looks for evidence of RNA from SARS-Cov-2 in the patient’s airways. If the test finds this genetic material, it’s typically a solid sign that this person is actively infected with Covid-19. However, as this new data highlights, that’s not necessarily the case. Inactive debris of viral cells might still be lurking in the body even after the tissue is clear, for example, and flag up a positive result. In other words, re-positive cases perhaps say more about the shortcomings of the testing than the disease itself. 

All of these conclusions were based on data gathered by health authorities in South Korea, not a peer-reviewed study. Although this means the conclusions still need further scrutiny, it’s some of the best evidence available on the issue yet. As mentioned, there was some anxiety regarding the reports of reinfection and re-positive cases, not least because health authorities were stumped by what it meant.

Dr Mike Ryan, executive director of WHO’s emergency program, said on April 13:  “With regards to recovery and then reinfection, I believe we do not have the answers to that. That is an unknown.”

“There are many reasons why we might see reactivation of infection either with the same infection or another infectious agent,” Ryan added. “There are many situations in viral infection where someone doesn’t clear the virus entirely from their system.”

Off the back of this new data, health authorities in South Korea have announced they will no longer consider people who have already been infected with Covid-19 as at risk of another infection.

“Based on the findings, starting 0:00 of 19 May, KCDC has stopped applying the previous protocols for the management of confirmed cases after discharge from isolation and for the management of re-positive cases. Under the new protocols, no additional tests are required for cases that have been discharged from isolation,” the KCDC said in a statement. 

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