Why are Recovered Coronavirus Patients Retesting Positive for the Virus?

L. J. Young

Recovered coronavirus patients are retesting positive for the virus according to the Korea Centers for Disease Control and Prevention (KCDC).

Does COVID-19 Reactivate?

As of Tuesday, May 5, 277 recovered patients who originally tested negative for the virus retested as positive during a subsequent test. The KCDC previously feared that the COVID-19 virus became reactivated after formerly going dormant.

On Tuesday the country’s infectious-disease experts concluded that the positive test results were false: a result of fragments of the virus that remained in patients’ bodies showing up in test kits. There was no live virus present in all 277 cases.

False Positives?

Dr. David Denning, Professor of Infectious Diseases in Global Health at The University of Manchester’s Division of Infection, Immunity and Respiratory Medicine, told InsideOver that the method of testing for the virus in formerly infected patients can produce false positives.

“Almost testing for the SARS CoV2 is done by detecting RNA (nucleic acid) using PCR (reverse transcription polymerase chain reaction), not by viral culture,” Denning said.

“PCR is highly sensitive and in the category level 3 labs in which it is done, it is possible some low level lab contamination of RNA occurred, which produced false positive results.

“It is equally likely that patients recovering from infection have a few residual cells containing dead virus that are picked up by the PCR assay,” Denning added.

This refutes theories in the scientific community that the coronavirus can be reactivated or reinfected in former patients. Withal, the false positives seem to be good news for the future of herd immunity, as countries worldwide begin to lift quarantine restrictions.

There are now over 3.6 million cases of coronavirus worldwide, as of May 5, 16:00 BST. Nearly 1.18 million people have, in turn, recovered. One of the first nations to report a COVID-19 outbreak, South Korea has reported only 254 deaths as of May 5. Out of more than 10,800 confirmed cases, the country has seen 9,283 recovery cases so far.

This is because the country enforced one of the world’s most effective pandemic strategies, using contact tracing and widespread testing. Although it did not close most venues, the country’s leaders implemented mass social distancing guidelines to keep people apart.

The Future of Herd Immunity

Denning remains cautious about the future of herd immunity. “It is likely that symptomatic patients with COVID-19 develop partial or complete immunity to SARS CoV2,” he said.

“One way this is measured is with neutralising IgG antibody in blood. Other arms of the immune system are probably important, including saliva antibody (sIgA), T cells and probably natural killer cells.

“These parts of the immune system are a little hard to measure in terms of documenting herd immunity,” he continued, adding that “complete immunity means no chance of re-infection. Partial immunity means a possible chance, if exposed to lots of virus, and/or a milder infection. The term herd immunity would apply to both.”

Herd Immunity Isn’t Enough

Like other practices executed to defeat the virus, herd immunity is not a complete strategy on its own. Denning argues that the success of herd immunity will rest in “sustained immunity”.

“It is not clear to what extent those with asymptomatic SARS CoV2 (i.e. without the disease COVID-19) develop immunity and whether this immunity is partial or complete,” Denning said.

“It is also not clear how sustained immunity will be over time – other coronavirus immunity lasts a few months or years,” he added.

Experts around the world have warned of a second wave of the coronavirus as countries relax their lockdowns. As the search for a vaccine continues globally, experts also remain cautious and pessimistic about finding a vaccine soon. They have also called for renewed efforts towards identifying possible cases, tracing contacts, and monitoring symptoms.