Question: The South Korea CDC stated earlier this week that COVID-19 may “reactivate” in cured patients. How much of an issue do you think this is?

Answer: This issue of reactivation has come up a bit in the last few weeks. Back in our Q&A of 3/30, I shared an NPR story about four Wuhan residents who had recovered from COVID-19 and tested negative for the virus, but then tested positive several days later. There’s also a new article coming out of Zhongnan Hospital in Wuhan that explores of 55 patients who had been hospitalized with laboratory confirmed SARS-CoV-2 pneumonia. Of those patients, 5 (9%) who were discharged presented with SARS-CoV-2 reactivation. The authors state, “The reactivated patients included 1 asymptomatic patient and 4 symptomatic patients, which suggests the reactivation potential of asymptomatic or minimally symptomatic patients. The time from SARS-CoV-2 negative to positive ranged from 4 to 17 days, suggesting that recovered patients still may be virus carriers and require additional round of viral detection and isolation.” The authors did not find any clinical markers that were predictors of reactivation. The WHO confirmed today that it is investigating these reports, stating, “We are aware that some patients are PCR positive after they clinically recover, but we need systematic collection of samples from recovered patients to better understand how long they shed live virus.” Ugh! Yet another COVID-19 mystery to explore. I have no idea how big of an issue this could be, but the initial findings are concerning.

Finally, if you want to understand more about how viral reactivation works, here’s a scientific overview and here’s a quick synthesis — Basically, viruses can go through three different phases of replication — lytic (super productive replication), latent (dormant phase, which is uncommon for most human viruses), and persistent (slow replication that does little damage to host cells). Most human viruses replicate in lytic phase and a few viruses, like hepB are persistent. Herpes is the most common type of virus that has a latent phase. I am not aware of any research showing that coronaviruses have latent periods. I’m glad to know WHO and others are investigating!