Carol Shoshkes Reiss, a professor of Biology and Neural Science at New York University, said: "Although somebody can recover and no longer be infectious, they may still have these little fragments of [inactive] viral RNA which turn out positive on those tests".
The "re-infected" patients weren't able to spread any lingering infection they have.
Of 790 contacts of the 285 cases where a person tested positive again, no case was found that was infected exclusively from contact with relapse cases during relapse period.
Samples were taken from about 100 patients who had relapsed.
The South Korean government will allow third-year high school students to come to school every day, as it is their final academic year before they proceed to college or start working. Moreover, a PCR test can not distinguish between dead and active virus particles.
After these new findings, South Korea authorities revised their protocols, which said that people who recovered from coronavirus and completed their isolation period need not test negative before returning to their activities.
As of Tuesday, more than 400 people have reconfirmed cases of the virus, according to the KCDC. "We have not found evidence that those cases are contagious".
A research conducted by the Korean Centres for Disease Control and Prevention in South Korea shows that people who test positive within weeks of recovering from coronavirus aren't capable of transmitting the infection.
"Under the new protocols, no additional tests are required for cases that have been discharged from isolation", researchers said.
Instead, these people will be referred to as "PCR re-detected after discharge from isolation". Nearly all of the cases for which blood tests were taken had antibodies against the virus.
They also don't know how long immunity will last.
Students in South Korea are returning to schools for the first time since the coronavirus pandemic started rattling the nation.
One idea has been to issue "immunity passports" or "risk-free certificates" to people who were infected but later tested negative.
But the World Health Organization (WHO) advised against this and said the accuracy of such documents could not be guaranteed.
"Some governments have suggested that the detection of antibodies to the SARS-CoV-2, the virus that causes COVID-19, could serve as the basis for an "immunity passport" or 'risk-free certificate" that would enable individuals to travel or to return to work assuming that they are protected against re-infection, ' the World Health Organization said in a statement.
"We can proceed with in-person classes when students and staff are safe from COVID-19".
Here’s How Apple iPhone 12 Pro Max Might Look Like
The iPhone SE is smaller than the iPhone 11 series, with a 4.7-inch screen with bezels and a Touch ID button instead of Face ID. Available in three storage variants, the base 64GB model is priced at $399, while a 128GB variant could set you back $449.