Researchers find evidence that patients who tested positive for coronavirus after recovery may not be able to transmit the infection and may have antibodies that prevent them from falling ill again.
Scientists from the Korean Centers for Disease Control and Prevention examined 285 Covid-19 survivors who tested positive for the coronavirus after their disease subsided, according to a previous negative test result. The so-called re-positive patients were not found to have spread persistent infection and virus samples collected from them could not be grown in culture, suggesting that the patients did not deliver infectious or dead virus particles.
The results, reported late Monday, are a positive sign for regions that want to open up as more patients recover from the pandemic that afflicts at least 4.8 million people. The emerging evidence from South Korea suggests that those who have recovered from Covid-19 are not at risk of spreading the coronavirus if the physical removal measures are relaxed.
The results mean that South Korea's health authorities no longer consider people to be infectious after recovery from the disease. Investigations in the past month have shown that so-called PCR tests for the nucleic acid of the coronavirus cannot distinguish between dead and viable virus particles, which may give the wrong impression that someone who tests positive for the virus remains infectious.
Research could also help debate antibody tests that look for markers in the blood that indicate exposure to the novel coronavirus. Experts believe that antibodies are likely to offer some protection against the virus, but they still don't have solid evidence. They also don't know how long immunity can last.
A recent study in Singapore showed that recovered patients with severe acute respiratory syndrome [SARS] had "significant levels of neutralizing antibodies" nine to 17 years after initial infection, according to researchers such as Danielle E. Anderson from Duke-NUS Medical School.
Other scientists have found higher IgM levels, an antibody that occurs in response to exposure to an antigen in children, according to an article published on medRxiv. This suggests that younger populations have the potential to become more resistant to Covid-19. The study was not certified by peer review.
Based on the results of the South Korea study, the authorities said that after revised protocols, people should no longer be forced to test negative for the virus before returning to work or school after recovering from their illness and completing their isolation phase .
"The new protocols do not require additional testing for cases that have been released from isolation," the Korean CDC said in a report. The agency said it will now refer to "re-positive" cases as "PCR redetected after isolation."
Some coronavirus patients tested positive for the virus again up to 82 days after infection. Almost all cases for which blood tests were carried out had antibodies against the virus.