Scientists from the Korean Centers for Disease Control and Prevention studied 285 Covid-19 survivors who had tested positive for the coronavirus after their illness had apparently resolved, as indicated by a previous negative test result. The so-called re-positive patients weren’t found to have spread any lingering infection, and virus samples collected from them couldn’t be grown in culture, indicating the patients were shedding non-infectious or dead virus particles.

The findings, reported late Monday, are a positive sign for regions looking to open up as more patients recover from the pandemic that has sickened at least 4.8 million people. The emerging evidence from South Korea suggests those who have recovered from Covid-19 present no risk of spreading the coronavirus when physical distancing measures are relaxed.

The results mean health authorities in South Korea will no longer consider people infectious after recovering from the illness. Research last month showed that so-called PCR tests for the coronavirus’s nucleic acid can’t distinguish between dead and viable virus particles, potentially giving the wrong impression that someone who tests positive for the virus remains infectious.

South Korean authorities said that under revised protocols, people should no longer be required to test negative for the virus before returning to work or school after they have recovered from their illness and completed their period of isolation.

“Under the new protocols, no additional tests are required for cases that have been discharged from isolation,” the Korean CDC said in a report. The agency said it will now refer to “re-positive” cases as “PCR re-detected after discharge from isolation.”

Some coronavirus patients have tested positive again for the virus up to 82 days after becoming infected. Almost all of the cases for which blood tests were taken had antibodies against the virus.