From infancy through to old age, the microbiome plays an important role in modulating the host-immune system. As we age, our immune system and our gut microbiota change significantly in composition and function, which is linked to an increased vulnerability to infectious diseases and a decrease in vaccine responses. Our microbiome remains largely stable throughout adulthood; however, aging causes a major shift in the composition and function of the gut microbiome, as well as a decrease in diversity. Considering the critical role of the gut microbiome in the host-immune system, it is important to address, prevent, and ameliorate age-related dysbiosis, which could be an effective strategy for preventing/restoring functional deficits in immune responses as we grow older. Several factors, such as the host's genetics and nutritional state, along with the gut microbiome, can influence vaccine efficacy or reaction. Emerging evidence suggests that the microbiome could be a significant determinant of vaccine immunity. Physiological mechanisms such as senescence, or the steady loss of cellular functions, which affect the aging process and vaccination responses, have yet to be comprehended. Recent studies on several COVID-19 vaccines worldwide have provided a considerable amount of data to support the hypothesis that aging plays a crucial role in modulating COVID-19 vaccination efficacy across different populations.
Keywords: COVID-19; aging; gut microbiome; host-immune system; pandemic; vaccine response.