Requiring recovered COVID-19 patients to undergo tests before they return to work could be a waste of time, according to a new study.
There have been concerns contracting the virus doesn't confer immunity, with people testing positive for it weeks after they've recovered - sometimes even after negative test results.
But doctors in South Korea, one of the first countries outside of China to experience an outbreak of the deadly disease, say it appears the positive tests can't tell the difference between active and dead virus particles.
They looked at 285 people who'd tested "re-positive" after recovering from COVID-19, which has killed almost 330,000 people worldwide.
They traced 790 contacts of those people, and found only three new cases of COVID-19 among them - all of whom had contact with members of the secretive Shincheonji church, which was at the centre of the nation's outbreak in February. None caught the disease off any of the re-positive patients.
Viral samples taken from 108 of the re-positive patients weren't able to be grown in lab cultures, suggesting they were dead.
Antibodies for the disease were found in all 285 patients, further evidence immunity is possible after an infection.
The Korean Centers for Disease Control and Prevention (KCDC) said it would now stop recommending those who test positive for COVID-19 a second time go into self-isolation, as it had been.
"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."
In other words, once they've recovered from the illness, South Koreans are good to go back to work without fear of infecting others.
The World Health Organization in April warned against countries issuing 'immunity passports' to people who'd recovered from the disease, saying there was no evidence getting infected conferred immunity.