Some test positive for COVID-19 twice. So why do experts say reinfection is unlikely?
As China and Japan start to reopen after being shuttered by the coronavirus pandemic, doctors are finding that some patients are testing positive a second time, worrying many that immunity is impossible.
Some experts say the answer lies in faulty tests, but others have said the virus could be reactivating in people’s bodies.
Health officials in South Korea, however, say the sensitive tests just cannot tell the difference between a virus that is dead and a virus that still lives, according to the Korea Herald.
“COVID-19 is the most challenging pathogen we may have faced in recent decades,” Korea Centers for Disease Control and Prevention (KCDC) Deputy Director Kwon Joon-wook said, according to CNN. “At the moment, we think that there is no danger of further secondary or tertiary transmission.”
On the other hand, the World Health Organization said that as of April 24, no study has shown that the presence of antibodies — proteins that fight off pathogens — to the virus means you are protected from reinfection.
Most studies demonstrate that people who recover from the virus have antibodies, but in some patients, there are “very low levels” of them in their blood, WHO said in a statement.
“At this point in the pandemic, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an ‘immunity passport’ or ‘risk-free certificate,’ ” WHO said. “People who assume that they are immune to a second infection because they have received a positive test result may ignore public health advice.”
As of Sunday, 263 South Koreans tested positive for COVID-19 — the disease the virus causes — a second time after being told they were virus-free, the Korean Herald said.
But Kwon said that so far, there is no evidence of a person who has tested positive a second time spreading the disease to others, CNN reported.
Is it dead or alive?
The test used to detect the coronavirus in a patient is called polymerase chain reaction (PCR), and its job is to find evidence of a virus’s genetic information in a patient sample, such as a throat or nose swab.
The test has its technical limits, Oh Myoung-dona, a Seoul National University hospital doctor, said at a news conference at the National Medical Center in South Korea, the Korea Herald reported.
The test cannot tell if the remaining virus cells in a person — which can be detected one to two months after the cell dies — is dead or alive, Oh 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,” Carol Shoshkes Reiss, a professor of Biology and Neural Science at New York University, told Live Science.
To back up the claim, scientists culture the virus, meaning they place the virus in a dish and see if it grows on its own, Reiss told the outlet. If someone has been reinfected after testing negative, then their culture sample will grow.
The KCDC investigated three cases from the same family where some members tested positive after recovering, according to CNN.
“In each of these cases, scientists tried to incubate the virus but weren’t able to — that told them there was no live virus present,” the outlet reported.
How the virus infects our cells matters, too
Research shows the coronavirus does not “infiltrate the nucleus, or core of the cell,” but rather it stays on the outside of it, doctors said at the news conference, the Korea Herald reported.
“This means it does not cause chronic infection or recurrence,” Oh said, according to the outlet.
This is unlike the human immunodeficiency virus (HIV) and the chicken pox virus, Reiss told Live Science. These pathogens take over a person’s genome, or genetic material, by going into the nucleus where they hide harmlessly.
Years later, they can reactivate, meaning the person will start to show and feel symptoms, Reiss said.
The coronavirus is not equipped to do this, experts agree.
Mutations are occurring slowly
Another theory behind the recent false-positive test results is that the virus is mutating, so the test cannot identify it.
But several studies show the virus is mutating slowly, and the changes that are happening are too “tiny” to be able to infect someone a second time, Reiss told Live Science.
“The genetic changes would have to be substantial enough that a person’s existing antibodies to SARS-CoV-2 would no longer work against a new strain,” the outlet said.
Reiss believes the virus will behave like the chickenpox, “imprinting on the host” immune system in a way that will protect them from the virus if exposed again, even if their levels of antibodies drop over time.
But she doesn’t know if reinfection is possible in the future.
“We don’t know what’s going to happen a year from now, nobody has that kind of crystal ball,” Reiss said.
This story was originally published May 1, 2020 at 12:31 PM with the headline "Some test positive for COVID-19 twice. So why do experts say reinfection is unlikely?."
