The study, released by the Korean CDC on Monday night, showed that 285 patients who still tested positive for the coronavirus despite apparently recovering were unable to spread any infection.

Additionally, virus samples taken from the group did not grow in culture, confirming the positive test was picking up non-infectious or dead virus particles. Last month, researchers found that polymerase chain reaction (PCR) tests for Covid-19’s nucleic acid did not distinguish between dead and viable virus particles, suggesting that someone who tests positive post-recovery could be no longer infectious.

In light of the new information, the Korean CDC is no longer requiring that individuals test negative before returning to work.