Schematic outlining the inter- and intra-island processes of livestock in the mathematical model.

To evaluate the effect of vaccine control measures against Rift Valley fever virus (RVFV), we developed a mathematical model to describe RVFV infection in livestock (cattle, sheep and goats). (A) In the model, animals moved between the four islands in the Comoros archipelago—Grande Comore (red), Mohéli (blue), Anjouan (green) and Mayotte (purple)—as governed by the livestock trade network as shown. The administrative boundary data were made available under CC BY 3.0 [ 22 ] and CC BY-IGO [ 23 ] licences. The CC BY 3.0 licensed the data for Mayotte [ 24 ], and the CC BY-IGO licensed the data for the Comoros [ 25 ], Tanzania [ 26 ], Madagascar [ 27 ] and Mozambique [ 28 ]. All presented data was unaltered. (B) The livestock population of each island was divided into compartments defined by infection status, vaccination status, and age. The diagram shows the compartments (squares) and the direction of transfer of livestock between compartments (arrows). The compartments eligible for vaccination depended on whether or not livestock were tagged (black circles) or not (white circles). The notation in each compartment defines the infection status (horizontally arranged) of the animals: susceptible to the virus ( S ), infected but not yet infectious ( E ), infectious ( I ) or recovered with life-long immunity to reinfection ( R ). The superscripts denote the vaccination status (vertically arranged) of animals: unvaccinated ( U ), vaccinated with developing protection ( and ), or vaccinated and partially protected from infection ( W ). The transitions between compartments of different age groups (diagonally arranged) are not drawn for illustrative purposes.