Antibody response induced in mice immunized by M2e5x VLP PLGA NPs using dissolving MNs. (A) Images of M2e5x VLP-loaded PLGA NPs incorporated into fast-dissolving microneedles. Study timeline with immunizations in weeks 0 and 3, blood collection in weeks 1, 4, and 7, sublethal challenge in week 8, and sacrifice and organ harvesting in week 10. (B) M2e-specific binding of serum from mice immunized with M2e5x VLP in suspension, in PLGA nanoparticles, or in PLGA nanoparticles with Alhydrogel® + MPL-A® PLGA NPs. Fluzone-coated wells were used to assess the binding of serum from Fluzone-immunized mice. (C) M2e-specific IgG1 and IgG2a serum binding. (D) M2e-specific IgA binding in the serum of immunized mice. Data are presented as the mean ± SD. Comparisons are made between M2e5x VLP and M2e5x VLP NPs and M2e5x VLP + Alhydrogel® + MPL-A® PLGA NPs. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001, and “ns” indicates not significant.