Floss-based vaccination targets the gingival sulcus for mucosal and systemic immunization.

The oral cavity is an accessible site for vaccination, but its sublingual and buccal sites have limited vaccine uptake. Here we show that flat tape dental floss can deliver vaccines through the junctional epithelium of the gingival sulcus, exploiting its naturally leaky properties. Floss-based vaccination delivered protein, inactivated virus, peptide-presenting immunogenic nanoparticles and messenger RNA. In mice, gold nanoparticles functionalized with a peptide derived from the ectodomain of the transmembrane matrix 2 protein of human influenza virus stimulated local lymph nodes, increased CD4+T cells in lymph nodes, lungs and spleen, and boosted antibody-secreting cells in the bone marrow. Floss-based immunization induced strong and sustained immune activation across multiple organs, robust systemic and mucosal antibody responses, and durable protection against lethal influenza infection, independent of age, food and liquid consumption. Floss-based vaccination was superior to sublingual and comparable with intranasal vaccination. In human participants, fluorescent dye delivered via floss picks effectively reached gingival sulcus, supporting clinical feasibility. These findings establish floss-based vaccination as a simple, needle-free strategy that enhances vaccine delivery and immune activation compared with existing mucosal immunization methods.