Every public health system faces a resource constraint. The question is never "would universal coverage be better?" — of course it would. The question is: "given finite resources, which investments deliver the most early-warning value?"
For aircraft wastewater surveillance, the Vespignani group at Northeastern University answered this question with extraordinary precision in a 2025 Nature Medicine study [1]. Their answer challenges the intuition that more airports always means better surveillance — and it has direct implications for where Bangkok sits in any future global network.
The model
The researchers built a computational model of global pandemic spread coupled with a model of the global air travel network. They then simulated more than 150,000 pandemic scenarios — different pathogen characteristics, different outbreak origins, different initial spread rates — and asked: for each scenario, how many airports need to monitor wastewater, and which ones, to achieve timely detection?
The scenarios varied from highly transmissible pathogens like a hypothetical influenza pandemic to slower-spreading coronaviruses. They tested networks ranging from 1 sentinel airport to full global coverage at every major hub.
The diminishing returns finding
The headline result: testing only 20 airports detects outbreaks approximately 20% slower than full global coverage [1]. This is a counterintuitive finding. Twenty airports, out of several hundred major international hubs, captures nearly the same early-warning value as monitoring the entire network — because pandemic spread is not random. It follows the structure of the aviation network.
The international aviation network is not uniformly connected. A small number of airports — typically the highest-traffic, most highly connected hubs — account for a disproportionate share of global connectivity. These are the airports where the most routes converge, where the most passengers transfer, and where a novel pathogen is most likely to pass through on its way to global spread.
Adding sentinel sites beyond a critical network size — the paper estimates this at roughly 15–25 airports — produces rapidly diminishing returns. A network of 100 sentinel airports detects outbreaks only marginally faster than a network of 20, but costs five times as much to operate.
The super-spreader airport concept
The model identified what the researchers called "super-spreader" airports — hubs whose centrality in the aviation network gives them outsized influence on global pathogen spread. These are not necessarily the largest airports by passenger volume; they are the airports with the highest betweenness centrality — the airports that lie on the largest number of shortest paths through the aviation network.
Major hubs like London Heathrow, Dubai International, Singapore Changi, Frankfurt, Hong Kong, and a small number of others appear consistently in these analyses as the most valuable sentinel sites. Suvarnabhumi (BKK) is consistently identified in network analyses as the primary hub for Southeast Asian connectivity — the airport through which the greatest number of regional routes pass.
A global network of 15–20 airports that includes BKK provides surveillance coverage of the region's air traffic that is qualitatively different from what is achievable without it. Bangkok's absence from such a network is not a gap in geography — it is a gap in the network's ability to model Southeast Asian spread dynamics.
The investment implication
The Nature Medicine study's diminishing returns curve has a direct financial corollary. The value of the first 20 sentinel sites in a global network is enormous — they capture the majority of early-warning benefit. The value of site 21, 22, and 23 is substantially smaller.
For governments deciding where to invest, this means that joining the global surveillance network early — as one of the first 20 sentinel sites — is not just a health security contribution. It is the moment when a national investment produces global value. Site 21 in a 21-site network is less consequential than site 5 in a 5-site network.
Thailand, through Bangkok, has a credible claim to one of those first 20 positions. The network science says so. The question is whether the investment decision is made while those positions are still being filled.