The Role and Delicate Balance of Host Immunity in Coronavirus Disease-19

Severe Acute Respiratory Syndrome (SARS) associated with SARS-CoV-2, causes a severe form of the respiratory illness known as Coronavirus Disease-19 (COVID-19). COVID-19 has emerged as a worldwide pandemic with a high number of fatalities. Approximately 112,654,202 people have been infected so far with this disease which has led to the death of more than one point seven million (2,496,749) till 24th Feb, 2021. Measures to counter this disease have led to a global economic slowdown. Multiple drug trials are ongoing and several putative candidates for vaccination against the virus have been approved and are in the pipeline. Many studies have also characterized the immunological profile of patients infected with COVID-19. Some studies suggest that the severity of the COVID-19 infection is directly associated with the cytokine storm. In this review, we aim to compile the available knowledge and describe the nature of immune responses in patients infected with COVID-19 infection in different age groups, comorbidity, and immune-compromised state and their association with disease severity.