# Impact of network structure on contagion

Network structure can have a drastic impact on how disease or information spreads. If there exists large hubs that can instantly spread something to many, they tend to dominate the dynamics. For instance, in an infinite Scale free network, the Epidemic threshold vanishes (Pastor Satorras2001epidemic)

The effect of large hubs is primarily due to the Friendship paradox. Whenever we choose a random neighbor in the network, we sample nodes preferentially to their degree (if connections are random enough). An analogous phenomenon would happen at much larger scale. For instance, Stier2021early argued that the attack rate increases with city size.

Also, Social contagion and biological contagion influence each other (Bauch2013social). Homophily and influence can produce pockets of vulnerable people that are connected to each other (Salathé2008effect).