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We still don’t know why some people can test positive for COVID-19 twice. Getty Images
  • The World Health Organization (WHO) says we don’t have enough evidence to understand if and why some people may experience reactivation after recovery.
  • We need more data to determine if and why the virus may be having a flare-up in some infected people.
  • But we may discover it’s all tied back to the functionality of each person’s immune system.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

South Korea recently reported that a significant number of people with COVID-19 have tested positive, then tested negative, only to test positive and experience symptoms, like fever, cough, sore throat, and fatigue, again.

Health officials in South Korea say it’s unlikely these patients got reinfected with COVID-19 a second time since they’re testing positive for a second time so soon, but rather that some people with COVID-19 may be experiencing a viral reactivation.

Health experts in the United States don’t think a reactivation of COVID-19 is likely since we’ve never observed viral reactivation in other coronaviruses.

It could very well be that the virus never left their system. It lingered, and they were never fully cured of the disease, and that’s what the subsequent COVID-19 tests are catching.

The World Health Organization (WHO) says we don’t have enough evidence to understand if and why some people may experience reactivation after recovery.

It’ll take time, and a lot of research, before we have a clear picture of the virus’s behavior.

“The truth is that we don’t exactly understand the dynamics of how people who test negative after initial infection end up testing positive again. We need more studies to clarify this observed phenomenon,” says Dr. Robert Glatter, an emergency physician at Lenox Hill Hospital in New York City.

Dr. Benjamin Neuman, a virologist and the head of the biology department at Texas A&M University-Texarkana, believes it’s not so much a reactivation of the virus as it is a resurgence.

Neuman thinks people are probably “being discharged with some virus still in them, and then the disease returns.”

Initial evidence from Hong Kong and China shows that the virus continues to be detectable in the lower lung and intestines anywhere from 2 weeks to a month, according to Neuman.

One study from Hong Kong looked at data from 59 people with COVID-19, as well as pooled data from more than 60 studies, and found “the presence of viral RNA fragments or particles in stool up to 33 days after initial infection with SARS-CoV-2, with no evidence of virus being detected in respiratory tract samples,” Glatter said.

This suggests traces or fragments of the virus are still lingering in other parts of the body, even if it’s not detectable through a nasal or throat swab.

We do see viral reactivation in other viruses, such as herpes and HIV. These viruses enter a dormancy period in which they become integrated into the host’s DNA.

After a period of time, the virus can become reactivated, potentially through stress like we see with chicken pox or shingles.

But coronaviruses like those that cause SARS, COVID-19, and MERS don’t have a dormant phase, and they don’t integrate into our DNA, making a reactivation unlikely.

“Human coronaviruses have not yet been shown to have anything like an inactive phase, so the idea of reactivation is a bit of a stretch,” Neuman said.

We need more data to determine if and why the virus may be having another flare-up in some infected people, but we may discover it’s all tied back to the functionality of each person’s immune system.

“It takes the coordination of the entire immune system to clear a viral infection, and it is an active struggle the entire time,” Neuman said.

Once the immune system is fighting the virus, there can be setbacks where the virus can temporarily gain the upper hand.

Where one person’s immune system can clear a virus quickly, it may take another person’s immune system over 2 weeks to get rid of it.

He suspects older people with COVID-19 who have weakened immune systems may be more likely to experience a resurgence — but, again, we need more research before any conclusions can be made.

According to Neuman, physicians in China aren’t releasing people with COVID-19 from the hospital until their fecal swabs produce negative results — something we’re not yet doing in the United States.

Because the virus seems to linger longer in the intestines, testing fecal matter gives doctors a better idea if the virus has officially been cleared from people’s bodies.

“Until we start doing that here, we won’t be able to tell the difference between reinfection, resurgence, or possibly reactivation of SARS-CoV-2,” Neuman said.

Antibody tests, which tracks who is partially or fully immune after recovering from COVID-19, can also help us control the community spread of the infection and potentially allow certain areas to ease social distancing restrictions.

But until we have those tests, Glatter says “we won’t have a good handle on the situation.”

South Korea recently reported that a significant number of COVID-19 patients have tested positive, then tested negative only to test positive and experience symptoms, like fever, cough, sore throat, and fatigue, again.

South Korean health officials suspect patients are experiencing a viral reactivation, but health experts in the United States don’t think a reactivation of COVID-19 is likely, since we’ve never observed viral reactivation in other coronaviruses.