A copy of the written consent is available for review from the Editor-in-Chief of this journal. Competing interestsThe authors declare that they have no competing likes and dislikes. Footnotes Publisher’s Note Springer Nature remains neutral with regard to jurisdictional statements in published maps and institutional affiliations.. of COVID-19 recurrence. reported five individuals with medical reactivation showing mostly with fatigue and fever, but none of them developed severe COVID-19 pneumonia or died [11]. Ravioli reported two seniors individuals who developed COVID-19, recovered and tested bad by PCR, and then developed a new COVID-19 pneumonia, with one patient dying and the additional remaining hospitalized at the time of the statement [12]. Lancman em et al /em . reported the case of a patient undergoing treatment for CD20-positive B-cell acute lymphoblastic leukemia who experienced a viral reactivation after receiving rituximab and other immunosuppressive chemotherapy [13]. The Korea Disease Control and Prevention Agency has documented 91 cases of recurrent contamination, and they emphasize the importance of viral reactivation especially in immunocompromised patients [4]. SARS-CoV-2 reinfection is usually another possibility in recurrent contamination. You will find 80 unique known genotypic variants of this computer virus; thus reinfection by another variant can lead to COVID-19 reinfection [14]. In a recent case series from the UK, six possible cases of recurrent contamination with the possibility of SARS-CoV-2 reinfection were reported, with patients exhibiting long intervals (84?days) between the ICI 211965 two COVID-19 episodes. In our patient, both the first and second events were moderate and showed no difference in symptom severity; similar clinical cases have been reported from Belgium, the Netherlands, and Hong Kong. These findings are contrary to those reported from Nevada (USA) and Ecuador, where secondary infection was severe [15]. The immunopathogenesis of SARS-CoV-2 entails both cell-mediated and humoral immunity, and the pathogenesis underlying reinfection is still under study. Reactivation is explained by the fact SARS-CoV-2 enters the lung cells via the angiotensin-converting enzyme 2 (ACE2) receptor. ACE2 receptors are expressed in nearly all human organs. In the respiratory system, ACE2 is mainly expressed in type II alveolar epithelial cells, but is usually ICI 211965 weakly expressed Mouse monoclonal to ERK3 on the surface of epithelial cells in the oral and nasal mucosa, indicating that the lower respiratory tract is the main target of SARS-CoV-2. ACE2 receptors are highly expressed in myocardial cells, kidney, and urinary bladder, and are abundantly expressed in the small intestine, especially in the ileum. The cell-free and macrophage-phagocytosed computer virus can spread to other organs and infect ACE2-expressing cells at other body sites [16]. Thus, even if COVID-19 patients become SARS-CoV-2-unfavorable by RT-PCR screening, there is still a chance that ICI 211965 the patient is harboring active computer virus that can reactivate at the first possible opportunity. Further, several studies have documented reinfection in COVID-19 patients with new strains of SARS-CoV-2 and have documented unique infecting strains using next-generation sequencing. Reinfection with variants of concern (including B.1.1.7 and B.1.351) has also been documented following contamination with wild-type computer virus [17, 18]. There is an urgent need for in-depth studies on recurrent COVID-19 infections in order to understand the factors, clinical conditions, and possibility of reinvasion of the computer virus in the human body. Theoretically, COVID-19 reinfection and reactivation can be recognized by whole genome sequencing of the SARS-CoV-2 computer virus in both the main and secondary episodes. In reactivation, the strain is the same, whereas in reinfection the strains are different. Recurrent COVID-19 is an emerging problem, and post-discharge and post-recovery surveillance of signs and symptoms in COVID-19-positive patients, with retesting for SARS-CoV-2 in those who present recurrent clinical manifestations of the disease, should be implemented. Further, it is important to stress to these patients the importance of maintaining the use of personal protective equipment and hand hygiene even after being cured of COVID-19. Acknowledgements None. Authors’ contributions JG analyzed the cases and collected the literature; JA prepared and edited the manuscript; AD performed molecular assessments; MS performed serology assessments and analyzed the results. All authors read and approved the.