COVID-19 vaccine-elicited immune mediators and their contribution to protective immunity

SARS-CoV-2, a highly transmissible virus triggered the COVID-19 pandemic inflicting devastating impact on public health and global economy; thus, the development of a vaccine was deemed the most efficient strategy. The immune system is a network of specialized cell types that interacts with cytokines to orchestrate protective responses. Until recently, investigators only evaluated vaccine efficacy with an emphasis on secreted antibodies, despite advancements in vaccinology no well-confirmed immunological correlates of vaccine-induced protection have been recognized. Technological and conceptual advances in cell-mediated immunology have resulted in numerous novel immunological signals, which could function as classifiers for vaccine-induced protection. Cytokine responses are essential for triggering and retaining humoral responses, which could potentially impact vaccination efficiency, thus, profiling might uncover vital information on the indicators of vaccine response and long-term protective variables. This integrated immunological approach to vaccine response provides a broader perspective and ensures an improved comprehension of the pathways and mechanisms involved. Here we aim to summarize the mechanism of action of the different vaccines developed and examine several immunological mediators associated with SARS-CoV2 immunization. We also provide insights, on new possibilities correlating with vaccine-induced immune responses and their effectiveness in defining protective immunity.