One of the nightmare scenarios for modern society is the possibility of a global flu pandemic like the 1918 Spanish influenza which infected about a quarter of the global population and killed as many as 130 million of them. 

An important question for policy makers is how best to limit the spread of such a disease if a new outbreak were to occur. (The Spanish flu was caused by the H1N1 flu virus that was also responsible for the 2009 swine flu outbreak.)

One obvious idea is to close international airports to prevent, or at least dramatically reduce, the movement of potentially infected individuals between countries. But is this the best approach?

Today, Jose Marcelino and Marcus Kaiser at Newcastle University in the UK, provide an answer. They say a better approach is to cut specific flights between airports because it can achieve the same reduction in the spread of the disease with far less drastic action.

These guys used a standard disease-spreading model to simulate the spread of an H1N1-type infection across a network consisting of the world’s top 500 airports and the flights between them. The disease started in Mexico City.

They then reran the simulation to see how different strategies could reduce the spread. They found that shutting entire airports can obviously reduce infection. 

But they also studied less obvious strategies such as looking for cities that play an important role in the network and reducing the flights between them by 25 per cent. This turned out to be a much more effective strategy.

They found that shutting entire airports only had a significant effect on spreading if it reduced travel by 95 per cent. By contrast,  they could achieve the same effect by removing just 18 per cent of flights between cities ranked by a network measure called edge betweenness.  

At best shutting entire airports could only cut infections by 18 per cent whereas removing specific flights reduced infections by up to 37 per cent. 

“Selecting highly ranked single connections between cities for cancellation was more effective, resulting in fewer individuals infected with influenza, compared to shutting down whole airports,” say Marcelino and Kaiser. This approach has the added benefit that it disrupts far fewer individuals 

Because these guys used a model of the actual global network of airports and flights they were able to identify the specific connections that would need to be targeted. For an infection that starts in Mexico City, the highest ranked routes that would need to be targeted are Sao Paulo to Beijing, Sapporo to New York and Montevideo to Paris.

That seems an eminently sensible suggestion. However, policy makers might want to study this approach in more detail to check that the conclusions still hold if outbreaks occur in other places too. 

Another idea worth checking is to see whether smaller airports could also play an important role in disease spreading.  Marcelino and Kaiser study a network consisting of the top 500 airports but the world is blessed with some 4000 airports in total. 

It’s not inconceivable that some of these could play a crucial role in linking different parts of the world in a way that could facilitate disease spreading. 

Ref: http://arxiv.org/abs/1205.3245: Critical Paths In A Metapopulation Model Of H1N1: Efficiently Delaying Influenza Spreading Through Fight Cancellation