For thousands of years this "event" has taken place, just not in plain site, not until now. What used to happen by moonlight on cobblestone streets and in the dense woods away from the modern world now takes place on a set date, at a set location. Over population and lack of seclusion in a technology driven, social media laden world has turned an event from purely survival, to spectator sport AND survival.
Citizen will run a given course, 5 kilometers in this case, and try to weave through the Vampires who have waited exactly one year for this feeding.
Vampires, a small and set in their numbers, will tend to their part of the course and try to "convert" as may citizens as they can by marking them with their blood in powder form (red corn starch).
After the running, the Vampires and Citizens convene for a truce between the two is agreed upon for the rest of the night until each of the Citizens has closed their eyes for the night. The blood powder marking allows the Vampires to track for their final feeding, long after the festivities end and often in the confines of the dreamers mind, which happens to be enough