Protective immunity to viral infections depends on the generation of long-lived antibody responses and memory B cells. Germinal centers in lymphoid tissues are the key sites where B cells undergo affinity maturation and differentiate into long-lived plasma cells and memory B cells. In this presentation, we examine the dynamics of germinal center responses following vaccination, with a focus on respiratory viruses, including influenza and SARS-CoV-2. Using approaches including fine-needle aspiration of human lymph nodes, our work tracks antigen-specific B-cell responses longitudinally in vaccinated individuals. These studies reveal not only how germinal center reactions shape the quality, durability, and breadth of antibody responses, but also how it is regulated by antibody feedback. Understanding the mechanisms that govern these processes provides critical insights for the rational design of next-generation vaccines that induce durable, broadly protective immunity.