The effectiveness of the immune responses to SARS-CoV-2

Abstract

SARS-CoV-2 is the causative agent of COVID-19 that ranges between mild, moderate and severe disease. The immune responses vary considerably at these stages and increase in complexity as the severity of the disease increases. As a result, COVID-19 patients were found to exhibit variable clinical manifestations which might be due to the critical imbalance in between the protective and the harmful role of the immune responses. Over a year and a half passed by since the COVID-19 pandemic started and we still need to accumulate more knowledge about the host immune responses to SARS-CoV-2. Such knowledge is in regards to their effectiveness in different age groups, duration of protection and specially long-term association with the clinical outcomes. Various factors were found to influence the effectiveness of such responses. In this review, the effectiveness and the variability of the immune responses to SARS-CoV-2 that involves the innate and the adaptive immune responses, factors that reduce the effectiveness of these responses such as antibody-dependent enhancement of the disease, lymphopenia, immunosenescence, young age, and their outcome among various symptomatic subjects are discussed.