This observational study, sponsored by Korea University Guro Hospital, aims to elucidate the relationship between gut microbiota and immune response to two prominent COVID-19 vaccines: BNT162b2 (Pfizer-BioNTech) and ChAdOx1 (Oxford/AstraZeneca). The findings could have significant implications for vaccine efficacy and personalized medicine, particularly in the context of varying immunogenicity among individuals. If successful, this research may lead to novel strategies for enhancing vaccine responses through microbiome modulation, potentially creating a new market for microbiome-targeted therapeutics in vaccine optimization. The competitive landscape includes ongoing research into microbiome interactions with other vaccines, necessitating diligence in monitoring emerging data and potential partnerships.