Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) leading to acute respiratory distress syndrome (ARDS). Understanding the evolution of the virus, and immune-pathogenic processes are critical for designing future therapeutic interventions. In this review, we collate information on the structure, genome, viral life cycle, and adult and pediatric host immune responses in response to SARS-CoV-2. The immunological responses are a prototype of the developmental origins of health and disease (DOHaD) hypothesis to explain the socio-geographic differences impacting the severity and mortality rates in SARS-CoV-2 infections. The DOHaD hypothesis identifies the relevance of trained innate immunity, age groups, and geography for effective vaccinations. As COVID-19 vaccines are being rolled out, it may be pertinent to assess population-based immunological responses to understand the effectiveness and safety across different populations and age groups.