Category: Epidemiology

Summary: Finding the commuter-bridge strength where two under-vaccinated school bands stop behaving as separate outbreak hotspots and merge into a broader epidemic mode.

Localized outbreaks can form around under-vaccinated age bands even when surrounding age groups are better protected. This experiment asks when two such school-centered hotspots, separated by more vaccinated age bands, become effectively fused because commuter contact between them is strong enough to create a broader outbreak mode.

The model builds dense next-generation operators for a dual-hotspot age structure and uses GPU iterative deepening to bisect the commuter-bridge threshold. The key measurement is where the leading epidemic mode sits: whether it remains concentrated in the two school bands or spills across the shared bridge into a wider structure.

That focus turns mobility into a localization problem, not just a reproduction-number problem. The result is useful for identifying when commuter coupling changes who effectively carries transmission across otherwise separated school-based hotspots.

Method: GPU dense symmetric eigensolves with iterative deepening and bisection on commuter-bridge coupling in age-structured next-generation operators.

What is measured: Critical commuter-bridge threshold, localization of the leading epidemic mode, hotspot fusion versus separation, and bracket width.