South Korea is investigating a number of cases in Daegu where patients have tested positive after recovering from COVID19 and testing negative.

They are trying to find out if this is reinfection or if the virus returned ( "re-activated") and what this involved.

Health officials conduct PCR tests on quarantined patients regularly and have found many cases where people test negative at first THEN test positive. They're looking into how infectious these patients might be at this stage.

Also, they've discovered that in some cases the PCR test will be positive even in those who have HAD the virus - (so those with antibodies for COVID19).

They're using samples from these patients to investigate how much immunity develops in patients who have already had COVID19