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Are we seeing COVID-19 reactivation, reinfection or something else?

A street in Seoul South Korea at night.

UPDATE: South Korean experts have confirmed that tests were showing false positives and not reactivation or infection of COVID-19. For further details see here.

A growing number of South Korean patients who have recovered from COVID-19, the infection caused by the new coronavirus (SARS-CoV-2), are suspected of showing signs of virus reactivation, according to the director of the Korea Centers for Disease Control and Prevention (KCDC), Jeong Eun-kyeong. In the space of one week in early April 2020, the number of suspected reactivation cases in South Korea jumped from just 51 to 116.

Has reactivation of SARS-CoV-2 in recovered COVID-19 patients been confirmed?

At the moment the KCDC believes that it may be seeing cases of SARS-CoV-2 reactivation in some people who were previously thought to have been cured of COVID-19. Reactivation of SARS-CoV-2 is suspected and may explain why 116 people who have recovered from COVID-19 and twice tested negative for SARS-CoV-2, have then gone on to test positive again shortly after being released from quarantine.

We currently have very little information about the group of possible reactivation cases. It’s not clear, for example, exactly how long they went before they tested positive again or whether their symptoms have returned. It’s also not clear whether they continue to test positive for any length of time.

Jeong has acknowledged that South Korea has seen many cases where patients test negative during treatment for COVID-19 and later test positive again. This is something that has been observed in other countries too. However, Jeong hasn’t shed much light on exactly why they think these new cases are examples of virus reactivation and not something else, other than to say they tested positive just a short time after their release from quarantine.

What other explanation could there be for testing positive after recovering from COVID-19?

Experts have put forward other theories to explain why patients seemingly cured of COVID-19 have gone on to test positive again. Their reasons include:

  • Faulty tests results - the initial negative results may not have been correct

  • Remnants of SARS-CoV-2, which aren’t capable of causing an infection, are simply being detected

  • Reinfection - the results of a study conducted in 175 patients in China who had recovered following mild cases of COVID-19, has reported that in 10 cases the patients had such low levels of COVID-19 antibodies that they could not be detected. This raises the possibility that some people could be infected with COVID-19 more than once.

When will we know more about SARS-CoV-2 reactivation?

Epidemiological and clinical studies are underway in South Korea to investigate the cases of possible SARS-CoV-2 reactivation. Determining whether these people are capable of infecting others is of particular interest. On April 10, 2020 it was reported that such testing could take about 2 weeks. A study investigating immunity following COVID-19 infection is also ongoing in South Korea.

In addition to South Korea’s efforts, the World Health Organization (WHO) has also announced that it will be investigating the possible cases of reactivation. Determining how long people continue to shed live virus after they recover from COVID-19, is an area that is also of particular interest to WHO.

Article references

  1. Reuters. South Korea reports more recovered coronavirus patients testing positive again. April 13, 2020. Available at: https://www.reuters.com/article/us-health-coronavirus-southkorea/south-korea-reports-more-recovered-coronavirus-patients-testing-positive-again-idUSKCN21V0JQ. [Accessed April 14, 2020].
  2. Bloomberg. Coronavirus May ‘Reactivate’ in Cured Patients, Korean CDC Says. April 9, 2020. Available at: https://www.bloomberg.com/news/articles/2020-04-09/coronavirus-may-reactivate-in-cured-patients-korean-cdc-says. [Accessed April 14, 2020].
  3. Wu F, Wang A, Liu M, et al. Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications. medRxiv. Available at: doi: https://doi.org/10.1101/2020.03.30.20047365. [Accessed April 14, 2020].
  4. The Korea Herald. 91 recovered COVID-19 patients test positive again: KCDC. April 10, 2020. Available at: http://www.koreaherald.com/view.php?ud=20200410000686. [Accessed April 14, 2020].
  5. Reuters. WHO is investigating reports of recovered COVID patients testing positive again. April 11, 2020. Available at: https://www.reuters.com/article/us-health-coronavirus-who/who-says-looking-into-reports-of-some-covid-patients-testing-positive-again-idUSKCN21T0F1?il=0. [Accessed April 14, 2020].