An update on COVID-19: SARS-CoV-2 life cycle, immunopathology, and BCG vaccination.

The causative agent of novel coronavirus disease (COVID-19) is severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The SARS-CoV-2 possesses RNA as a genetic material with 79% of the match with the bat SARS-CoV genome, which became epidemic in 2002. The SARS-CoV-2 peripheral Spike-Fc protein binds specifically to the ACE2 receptors present on bronchial epithelial cells and alveolar pneumocytes to downmodulates its expression which leads to severe acute respiratory failure. The disease is super infectious from human to human and the symptoms are similar to flu. The old aged and immunocompromised population are severely affected, and healthcare providers globally applied various strategies for treatment including the repurposing of drugs including antimalarial drug, hydroxychloroquine and anti-viral drugs. Herein, we described the SARS-CoV-2 pandemic, immune responses, possible drug targets, vaccines under the trials and correlated the possibility of trained immunity induced by BCG vaccination over control of SARS-CoV-2 infection. The countries with constraint BCG vaccination policy are struggling badly compared to countries with BCG vaccination policy. The BCG vaccination policy supports either lowering the total number of COVID-19 cases or the increasing recovery rate.