PHN Explores: In South Korea, a growing number of Covid-19 patients test positive after recovery (From NPR)
PHN Content By Mat Edelson
If We Had Written the Headline
The apparent reinfection of 163 recovered Covid-19 patients casts questions over long-term immunity
Why You Should Care
“Immunity” is the concept that recovered coronavirus patients will create and retain enough antibodies to prevent catching the virus again (or even if they do catch it twice, if partial immunity will keep people from getting very sick the second time around).
Obviously the hope is such immunity exists, but right now we don’t know. That’s why this story out of South Korea is so concerning. It could be that people recover and completely clear the virus from their bodies, only to become reinfected again. However, as the NPR story notes, it’s also possible these patients recovered from their symptoms, but still had a small amount of the virus circulating in their blood. This amount would be lower than the test could detect, creating what’s known as a “false negative” test result.
This idea of “false negatives” reinforces the notion, as suggested by the World Health Organization, that recovered Covid-19 patients not be discharged from the hospital until they receive negative findings on two tests taken 24 or more hours apart.
Dr. Jeong Eun-kyeong, director-general, (South) Korean Centers for Disease Control and Prevention
According to the CDC (and you’re not going to like this), rapid influenza diagnostic tests—similar to the type being tried with the coronavirus—have a false negative rate of between 50 to 70%. That’s not unusual. To quote from the FDA’S summary recently authorizing LabCorp’s Covid-19 test onto the market, “Negative (test) results do not preclude SARS-Cov-2 (Covid-19) infection.” Generally, doctors and researchers have far more confidence in these kinds of diagnostic tests ruling in an infection (a “positive” finding, meaning you have the virus) as opposed to ruling it out (a “negative” finding, meaning you don’t).
From Scientific American: What immunity to COVID-19 really means: The presence of antibodies to the SARS-CoV-2 virus could provide some protection, but scientists need more data.
It’s dense reading, but if you’re so inclined, here are links to the CDC’s guidelines on Rapid Influenza Diagnostic Tests