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Evidence of Severe Acute Respiratory Syndrome Coronavirus 2 Reinfection After Recovery from Mild Coronavirus Disease 2019

Our take —

In this study, conducted in three South Korean hospitals in early 2020, researchers investigated six individuals who retested positive for SARS-CoV-2 via RT-PCR after two consecutive negative results. Based on attempts to sequence samples from the initial and subsequent reinfection time points, the researchers concluded that one case had clearly been reinfected and five cases were clearing “dead” viral fragments from their original infection.

Study design

Case Series

Study population and setting

This study described six individuals from three South Korean hospitals with who were admitted with symptomatic COVID-19, had two consecutive negative RT-PCR results after recovery, and then later showed evidence again of SARS-CoV-2 via RT-PCR. Full length sequencing of the virus was attempted on samples from all positive time points, and phylogenetic analyses were performed on viable samples.

Summary of Main Findings

Individuals were majority female (66%) and a median age of 29.5 years (range: 17-72 years). Four patients were symptomatic at retest, one patient had no symptoms at retest, and one patient was lost to follow-up. One individual had clear evidence of reinfection, with phylogenetic analyses demonstrating the second viral infection to be from a distinct subgroup from the first. This patient was a 21 year old immunocompetent female, whose only comorbidities were allergic rhinitis and high blood pressure. This patient’s first infection was on March 11, 2020, and their second infection was on April 6, 2020 (i.e., 26 days apart). The other five patients had retest specimens without mappable whole genome sequences, which suggest that these samples contained “dead” virus fragments that were still being cleared after recovery — not viable viral RNA or a true re-infection.

Study Strengths

This study was methodologically strong and included sequence data at the time of both initial and supposed reinfection, allowing for longitudinal analyses of changes in viral genomes from the original infection to the positive retests.


The sample size of the study was limited – with only six individuals and 14 time points, so no conclusions can be made about how frequent reinfections may be. The authors also did not clearly specify the source population, and it is unclear whether these six participants represent all patients who had positive retests at these three hospitals or if they represent a subgroup.

Value added

This investigation clearly demonstrated that reinfections occur. These data also show that positive RT-PCR retests, which could be interpreted as a reinfection, may simply be “dead” virus fragments in the respiratory epithelial cells that have not yet been cleared by recovering patients.

This review was posted on: 30 July 2021