As more people start getting COVID-19, an important question for planning the coronavirus response is: can they catch it twice?

Some reports have suggested that some people who recover from COVID-19 can then test positive for the virus again shortly after. The limited research conducted so far suggests that this might be because of fluctuations in people’s viral levels rather than reinfection. This research only looked at 4 people, so the issue isn’t settled yet.

Because of the way our immune systems work, it seems unlikely that a person who has successfully fought off the novel coronavirus would get infected again in a short period of time. Initial research in monkeys supports this.

Some viruses like the flu can change enough to evade the immune system and infect people again and antibody levels can fade, but these things take time. It’s too early as yet to know how immunity to the novel coronavirus might develop or how the virus might change in the long term.

 

Where did the story come from?

In February a Japanese woman who had recovered from COVID-19 and tested negative for the virus, developed symptoms and tested positive again about 20 days later. China has also reportedly had similar cases. These cases led to people questioning whether it was possible to get the novel coronavirus twice.

 

What is the basis for the claim?

It’s very difficult to know for sure the reason behind the cases above. While reinfection is one explanation it is also possible that people’s infections never went away but were temporarily undetected. This might happen because viral levels were low.

A Chinese study has reported on the follow-up of 4 medical professionals after recovery from COVID-19 and testing negative for the virus. All had been treated with an antiviral drug used to treat flu (oseltamivir).

It found that all 4 had throat swab tests positive for coronavirus again 5 to 13 days after leaving hospital. None of them had symptoms or had any changes to their lungs at the time.

This is a relatively small number of mild to moderate cases, and it’s not possible to say for sure that the same would be seen in all cases. The researchers did thorough testing for the virus, carrying out multiple tests to check their results. They suggest that the findings reflected people still being carriers, as they had not been in contact with any other people with respiratory symptoms who could have reinfected them.

While the study suggests that the people may still have had coronavirus in their throats, we don’t know if they were producing enough to be infectious. None of the people living with them at the time caught coronavirus from them.

Early stage research in 2 rhesus monkeys who were infected with the novel coronavirus found that they did not catch it again when re-exposed a month later. This small study has not yet been checked for robustness by other researchers so is not conclusive.

 

What do trusted sources say?

The US Centers for Disease Control and Prevention (CDC) say that the immune response to the novel coronavirus is not yet understood. They say that people who caught the coronavirus that causes MERS were unlikely to be re-infected shortly after recovery, but that it is not yet known whether similar immune protection will be observed for patients with COVID-19.

This week the UK’s government’s chief scientific adviser Sir Patrick Vallance said that while some people do catch infectious diseases a second time, it is rare. He said there was no evidence to suggest that this would happen with the novel coronavirus.

Analysis by EIU Healthcare, supported by Reckitt Benckiser

 

Citations

  1. Coronavirus: Japanese woman tests positive for second time. The Guardian, 27 February 2020. https://www.theguardian.com/world/2020/feb/27/japanese-woman-tests-positive-for-coronavirus-for-second-time (Accessed 17 March 2020)

 

  1. Zhou L et al. [Cause analysis and treatment strategies of “recurrence” with novel coronavirus pneumonia (covid-19) patients after discharge from hospital]. Zhonghua Jie He He Hu Xi Za Zhi. 2020 Mar 2;43(0):E028. [Epub ahead of print] https://www.ncbi.nlm.nih.gov/pubmed/32118391 (Accessed 17 March 2020)

 

Reading list

  1. Lan L et al. Positive RT-PCR Test Results in Patients Recovered From COVID-19. JAMA. Published online February 27, 2020. https://jamanetwork.com/journals/jama/fullarticle/2762452 (Accessed 17 March 2020)
  2. Bao L et al. Reinfection could not occur in SARS-CoV-2 infected rhesus macaques. bioRxiv, 14 March 2020. https://www.biorxiv.org/content/10.1101/2020.03.13.990226v1.article-info (Accessed 18 March 2020)
  3. US CDC. Coronavirus Disease 2019. Healthcare Professionals: Frequently Asked Questions and Answers. Updated 17 March 2020. https://www.cdc.gov/coronavirus/2019-ncov/hcp/faq.html (Accessed 17 March 2020)