Solidified saturated fats coating subunit vaccines greatly extended vaccine booster release and contributed to a Th1/Th2 mixed immune response in mice.

Delayed release of vaccine coupled with a soluble vaccine acts as a primer and a booster with only a single administration, which would be very beneficial to livestock producers. We developed a subdermal pellet consisting of solid-phase pure stearic acid (SA) or palmitic acid (PA) that was used to encapsulate a small volume liquid vaccine consisting of fluorescently labeled *Ovalbumin (Cy5-*OVA) formulated with Emulsigen-D +/- Poly I:C (EMP) adjuvants. Mice were also immunized via the subcutaneous route with Cy5-*OVA-EMP (soluble liquid). The vaccine leached out of the pellet with very little dissolution of the fat itself resulting in the sustained subdermal delivery of antigens and adjuvants. Cy5-*OVA was still visible 60 days post administration in mice immunized with stearic acid-coated or palmitic acid-coated pellets. In these mice, persistently high IgG1 and IgG2a antibody titres were detected as well as significant IFNγ production at least 60 days post-injection. These responses were significantly higher than those observed after a single subcutaneous injection of the vaccine. A repeat trial with the pellets alone +/- the soluble vaccine showed comparable immune responses after surgical implantation of the pellet, suggesting that pellet alone may be sufficient. The PA-coated vaccines led to dermal inflammation in the mice that would limit usefulness of this vehicle, but this was largely absent when SA was used to coat the pellets. These data suggest that the SA-coated adjuvanted vaccine prolonged the release of the vaccine and triggered a comparable immune response to the mice that received the two liquid injections, and a single pellet vaccine should be tested as a novel immunization method for livestock.