**Abstract**

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) invades the host's cells via the angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine 2 (TMPRSS2). ACE2 and TMPRSS2 molecules are highly expressed on the respiratory tract but are also expressed in other organs such as kidneys, heart, and intestine, which could partially explain the multiple organ infection, damage, and failure. During the COVID-19 disease course, patients may develop a dysregulation in the immune response, with an exacerbated production of pro-inflammatory molecules and hypercoagulation, which can collaborate to the increase in tissue damage and death. This chapter will cover general aspects of the innate and adaptive immune response during COVID-19, the impact of comorbidities on the immune response to SARS-CoV-2, and the immune response generated by COVID-19 vaccines.

**Keywords:** SARS-CoV-2, COVID-19, immunology, immune response, inflammation
