(A, B) S2GΔHR2-presenting I3–01v9 SApNP vaccine distribution in a lymph node 12 h after (A) a single-dose or (B) prime-boost footpad injections (10 μg/footpad, 40 μg/mouse). A schematic illustration of SApNPs in lymph node follicles is shown. (C, D) Histological images of the S2GΔHR2 spike and S2GΔHR2-presenting E2p and I3–01 SApNP vaccine trafficking and retention in lymph node follicles 2 h to 8 weeks after (C) single-dose or (D) prime-boost injections, with a scale bar of 50 μm shown for each image. (E, F) Quantification of vaccine accumulation in lymph node follicles 48 h after (E) a single-dose or (F) prime-boost injections. Data were collected from more than 10 lymph node follicles (n = 3–4 mice/group). The data points are expressed as mean ± SD. The data were analyzed using one-way ANOVA followed by Tukey’s multiple comparison post hoc test. **p < 0.01, ***p < 0.001, ****p < 0.0001.