Methods

We conducted this systematic review to explore and investigate the validity of reported re-infected cases worldwide. For this purpose, we carried out systematic research in Pubmed, Embase, Scopus, and Cochrane databases. We present the final search strategy with the letter ā€œCā€ below:
  1. [reinfection] (Title/Abstract) OR [reinfected] (Title/Abstract) OR [second infection] (Title/Abstract) OR [re-positive] (Title/Abstract) OR [re-positive] (Title/Abstract) OR [recurrent] (Title/Abstract) OR [recurrence] (Title/Abstract) OR [relapse] (Title/Abstract) OR [relapsing] (Title/Abstract) OR [persistent PCR positive] (Title/Abstract) OR [persistent positive PCR] (Title/Abstract)
  2. [COVID-19] (Title/Abstract) OR [SARS-CoV-2] (Title/Abstract) OR [Novel Coronavirus] (Title/Abstract) OR [2019-nCoV] (Title/Abstract)
  3. [A] AND [B]
Upon retrieving the desired search results, three researchers screened the articles in a two-step process. The first step of this process involved general inclusion/exclusion criteria based on the title, abstract, and keywords of each study.
The main exclusion criteria in this phase were the following:
1) Abstracts and conference-abstracts without full-text articles
2) Ongoing projects and clinical trials yet to be published
3) Lack of published original data, including review articles, or editorials without providing any original data
4) Case-reports, case-series, and pre-prints
5) Irrelevant to the aims and scope of the study
6) The smaller study in the studies with a high suspect of population overlap between them
In the second phase, we carefully read through the full-text of the articles and included the eligible studies. Finally, peer-reviewed cross-sectional, clinical trials, case-control, and cohort studies from the beginning of January 2020 until late July 2020 were included in our study.