Post-coronavirus illness 2019 (post-COVID-19) syndrome has been identified in a number of patients who initially experienced symptoms during the initial stages of the 2019 coronavirus disease pandemic. Since SARS-CoV-2 is a respiratory coronavirus that induces COVID-19, lung damage is a common complication; however, many other cells & organs are typically harmed as well, resulting in a wide range of symptoms. Patients with mild to severe COVID-19 experience these long-lasting symptoms, however there is little published research on the possible pathophysiological reasons behind this disease. This comprehensive study aims to sum up & assess the biological evidence surrounding post-COVID-19 syndrome. The research reviewed up to August 30, 2021 was included in an integrated review using the methods developed by Whittemore & Knafl.