Advances in Mucosal Adjuvants for Influenza Vaccines

Vaccination is an effective way to prevent influenza virus infection. Currently, intramuscular vaccines are the most commonly used and can provide strong humoral immunity, but they may not induce the mucosal immune response well. A variety of pathogens gain access to the host via the respiratory tract, and the mucosa serves as the initial line of defense against bacterial invasions. Therefore, developing mucosal vaccines is a valuable strategy for preventing respiratory infectious diseases. The mucosal barrier hinders antigen delivery and immune activation, making efficient mucosal adjuvants crucial for vaccine advancement, though their use faces several obstacles. The main challenges faced by mucosal adjuvants are mucosal tolerance, delivery efficiency, and immune response balance. Future mucosal adjuvants will continue to focus on multitarget synergistic design and combination adjuvant application. The safety and efficacy of future influenza vaccines are contingent upon the judicious selection of suitable mucosal adjuvants. The creation of next-generation influenza vaccines will be made easier as our knowledge of adjuvants grows. In this review, we summarize the current progress and applications of mucosal adjuvants for influenza vaccines, with implications for the development of novel influenza vaccines and vaccines against other infectious diseases.