Some recovered covid-19 patients who again tested positive for the coronavirus likely weren’t reinfected after all. On Thursday, South Korean officials stated that there’s no evidence currently that the virus is reinfecting people in the country, and the test results that suggested reinfection were likely false positives finding dead virus particles.
South Korea is one of the few countries to have successfully contained covid-19 from the very beginning, thanks largely to an aggressive testing and contact tracing program that was able to isolate local outbreaks early on. For comparison, the U.S. and South Korea both reported their first covid-19 case on January 19. But even when taking population into account, the U.S. now has over 3,000 confirmed cases per million people, while South Korea has 200 confirmed cases per million, as of April 30. Overall, the country has reported around 10,000 cases and 247 deaths.
The wide availability of testing in South Korea has also meant that residents are tested even after they’ve seemingly recovered from the illness. A few of these patients, the country has reported, have tested positive for the virus once their symptoms had cleared and after they had been considered virus-free. These reports (which have occurred elsewhere as well) have raised the possibility that immunity to the virus may not be guaranteed and that immediate reinfection could happen. At last count, over 240 of these relapsed cases have been reported by South Korea.
But an expert committee assembled by the South Korean government said Thursday that there is little evidence for reinfection, based on their findings.
For one, the typical PCR (polymerase chain reaction) tests used to find the virus in people aren’t designed to look for “live” virus. Rather, they detect minute traces of viral RNA, genetic material that is then amplified in the lab. These traces can come from an active infection in a person, but they can also come from dead viral particles left behind in the body’s cells. And the latter is what seems to be happening, according to Oh Myoung-don, an infectious disease specialist at Seoul National University and head of South Korea’s central clinical committee for emerging disease control.
“The tests detected the ribonucleic acid [RNA] of the dead virus,” said Oh at a press conference Thursday, reports the Korea Herald. “The respiratory epithelial cell has a half-life of up to three months, and RNA virus in the cell can be detected with PCR testing one to two months after the elimination of the cell.”
Oh also said that it’s unlikely the virus is somehow reactivating in the body after an initial infection, which some doctors have theorised could explain the cases. Unlike some viruses that can lay dormant in the body, such as HIV, the coronavirus behind covid-19 doesn’t seem to directly hijack a cell’s command centre, the nucleus. “This means it does not cause chronic infection or recurrence,” Oh said.
Oh and his team’s conclusions should be verified by other researchers, but this is certainly a promising sign. That said, even if reinfection isn’t happening in these specific cases, it doesn’t mean it’s impossible for the virus to reinfect people down the line. Experts generally agree that surviving an infection should grant some degree of immunity, based on what we know about other human coronaviruses, but it’s unknown how long this immunity should generally last, and we still don’t have a reliable way to tell if and when someone is immune.