Beyond antigenic variation: A review of innovative immuno-epidemiologic approaches to trypanosomiasis vaccine design.

Trypanosomiasis remains a major neglected tropical disease, largely uncontrolled due to rising drug resistance and the absence of an effective vaccine. Decades of vaccine failure are primarily linked to the parasite's immune-evasion strategy of Antigenic Variation (AV), driven by continual switching of the Variant Surface Glycoprotein (VSG) coat. This review proposes an integrated immuno-epidemiologic framework that moves beyond VSG-focused strategies by targeting conserved functional vulnerabilities and incorporating population-level transmission dynamics. The approach redirects vaccine development toward invariant, indispensable antigens such as the Transferrin Receptor (TfR), Invariant Surface Glycoproteins (ISGs), and Paraflagellar Rod (PFR) components. Antibodies against these molecules can induce conserved killing mechanisms, including iron starvation or disruption of essential membrane functions - regardless of VSG switching. Advances in reverse vaccinology enable multi-epitope and mRNA platforms to encode these structurally constrained targets, while complementary transmission-blocking and vector-focused strategies aim to interrupt parasite development within tsetse flies. A central argument is that partially protective vaccines (PPVs) can produce substantial epidemiologic benefits by lowering parasitemia, shortening infectious duration, and reducing the probability of vector infection. Such effects can meaningfully suppress transmission without requiring sterilizing immunity. A One Health approach, coupled with realistic population-based efficacy metrics, is essential for future vaccine development. By exploiting conserved molecular constraints and integrating immunologic, ecological, and epidemiologic insights, this framework outlines a practical pathway toward effective trypanosomiasis vaccination.