Seasonal and pandemic influenza A viruses continue to pose a serious global health threat due to the limited mucosal protection induced and insufficient cross-strain immunity by the current vaccines. This dissertation focuses on the development of integrated vaccine strategies to enhance both systemic and mucosal immune responses, thereby achieving broad protection against influenza A viruses. To address these challenges, I designed and evaluated novel vaccination platforms that combine immunostimulatory adjuvants, nanoparticle delivery systems, and mucosal targeting. Lipid nanoparticles (LNPs) were fabricated to co-deliver influenza mRNA antigen and mRNA adjuvant encoding cytokines (fusion cytokine GIFT4, or CCL27). These mRNA-adjuvanted LNP vaccines elicited enhanced systemic antibody responses, germinal center reactions, and activation of both T and B cells, resulting in improved protection in murine models. To enhance mucosal immunity, a mucosal influenza protein nanoparticle (PNP) vaccine was developed combining with monophosphoryl lipid A (MPLA) and VSA-2, a novel semisynthetic saponin adjuvant. Intranasal delivery of this vaccine induced potent mucosal IgA responses, tissue-resident memory T cells, and long-lasting local and systemic immunity, while offering long-term cross-protection against influenza A viruses. Lastly, a polymeric mRNA delivery platform using biodegradable poly(β-amino ester) (PbAE) nanoparticles was formulated for intranasal administration. These PbAE-mRNA nanoparticles were efficiently taken up by antigen-presenting cells and activated innate responses in vitro. Intranasal PbAE-mRNA vaccination induced strong humoral and cellular mucosal immunity. A heterologous prime-boost strategy combining intramuscular mRNA LNP priming with intranasal polymer-mRNA boosting resulted in synergistically enhanced systemic and mucosal immune responses and complete protection against influenza A virus challenge. Collectively, this work demonstrates that combining mRNA adjuvants, mucosal adjuvants, and innovative mRNA delivery systems can overcome the limitations of current influenza vaccines by promoting robust and cross-reactive immunity in both systemic and local sites. These findings support a promising framework for the development of next-generation influenza vaccines and have broader implications for protection against other respiratory pathogens.