On Apr. 25, 2020, the World Health Organization (WHO) reported there was currently ‘no evidence’ that people who have recovered from COVID-19 and have antibodies are protected from a second coronavirus infection. In a scientific brief, the United Nations agency warned governments against issuing ‘immunity passports’ or ‘risk-free certificates’ to people who have been infected as their accuracy could not be guaranteed.

Coronavirus disease (COVID-19) is an acute infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and is characterized by high morbidity and mortality. COVID-19 outbreak began in China in December 2019 and spread rapidly worldwide, with the World Health Organization declaring it a pandemic on March 11, 2020. At present, 4,000,000 confirmed cases of COVID-19 have been detected in more than 200 countries, resulting in more than 280,000 deaths, and additional patients with COVID-19 are expected to be cured and discharged over time.

Prevention remains the focus for control of COVID-19, but the cured or recovered patients should not be ignored. Currently, little is known about cured COVID-19 patients, and there are no studies to clarify the infectious of the cured or guidelines regarding the management of these patients. However, it is very important to understand the clinical characteristics of cured patients, especially with respect to re-infection and person-to-person transmission.

A total of 296 patients were diagnosed with COVID-19 from January 20, 2020 to March 10, 2020. Among these patients, one died, two were still hospitalized, seven were under 18 years old, 48 refused to perform antibody test, and 51 were transferred or discharged to other hospitals for treatment. Altogether, 187 patients were screened and followed up at least once in our hospital and subsequently followed up till April 10, and they were included in the final analysis. The mean follow-up time was 45.7 days. No re-infection occurred in any patient after discharge and no medical staffs were infected during the treatment.

Out of these 187 patients, 35 (18.7%) patients showed positive results and 152 (81.3%) showed negative results for IgM. There were 154 (82.4%) patients with positive results and 33 (17.6%) patients with negative results for IgG. The antibody tests were performed after 53 days on an average from the date of disease onset. Of the 35 IgM positive cases, 12 cases turned negative during the follow up. PCR assays were undertaken in all patients using both pharyngeal and anal swabs. They yielded two positive pharyngeal swabs, seven positive anal swabs, and one positive result for both pharyngeal and anal swabs. On further retesting, all the positive results of PCR assays were found to be negative.

This study has the following limitations. Firstly, since this was an observational study, no interventions such as re-exposure of the cured patients to SARS-CoV-2 were performed. Therefore, it is hard to judge whether the cured patients were immune to the virus. Secondly, at the beginning of COVID-19 outbreak, there is no effective antibodies test, and the testing of antibodies were not performed at that time. So we could not compare the levels of antibody between hospitalization and follow-up. Thirdly, this was a single center study carried out in Guangzhou, a mild epidemic area. Accordingly, the conclusions of this study might not be suitable for extrapolation to other areas. Fourthly, our conclusions were based on a small sample size, which need to be further verified in a study with a large sample size. Nevertheless, our study results clarified some clinical features of the cured patients and maybe be of considerable importance for the prevention and control of COVID-19.

In our study, no evidence of person-to-person transmission was found in cured COVID-19 patients. There seemed to be no re-infection in the cured COVID-19 patients in Guangzhou. These finding suggest that the cured do not cause the spread of disease. Additionally, neither IgG nor IgM can be used to replace the PCR test in cured patient