The Importance of Different Social Networks for Infectious Diseases Fredrik Liljeros Stockholm University Karolinska institutet Supported by the Swedish Institute for Public Health and The Swedish Emergency Management Agency S-GEM
Stockholm Group for Epidemic Modelling, S-GEM Johan Giesecke SMI/KI Åkes Svensson SMI/SU Fredrik Liljeros SU/KI S-GEM
Why model epidemics? Will there be an outbreak? How many will be infected? The speed of the outbreak? How can we best limit the effects of an outbreak How many must be vaccinated? Who should be vaccinated? S-GEM
Outline Traditional Models Networks Empirical Network Studies S-GEM
Key Concepts Variation in number of contacts Assortative interaction Clustering/Transitivity Small World Network S-GEM
Epidemic models Deterministic models Stochastic models Agent-based models (Micro simulation models) S-GEM
A model should be as simple as possibly (But not to simple) S-GEM
Deterministic Models S-GEM
A very simplified example S-GEM Suceptible Infected
A simple differential equation- model S-GEM
Global saturation S-GEM
Our model is to simple capture global saturation S-GEM
We have to ad the number of susceptible into the model (K-I) S-GEM
It is possible to study important properties of deterministic models analytically S-GEM
The Basic reproduction rate, R 0 S-GEM
The SIS-model S-GEM
The SIS-model S-GEM
It is possible to let a deterministic model capture many relevant properties Individuals may become immune Individuals may die New individuals may be borned Individuals may belong to different groups with different type of behavior S-GEM
What are the implicit network assumptions in deterministic models S-GEM
Erdös-Rényi network (1960) Pál Erdös Pál Erdös ( ) S-GEM
Clustering/transitivity S-GEM
Clustering/transitivity S-GEM
Clustering/transitivity Suceptible Infectious S-GEM
Variation in number of contacts S-GEM
What do variation in number of contacts have on R 0 ? S-GEM
Assortative Interaction S-GEM
Struktural effects Variation in contacts Clustring assortativity Lower epidemic treshold Smaller outbreaks Slower outbreaks S-GEM
Why care about social networks? S-GEM
What do we know about structural properties of social networks? S-GEM
Collecting network data S-GEM
We can not use random samples S-GEM
Milgrams Study Nebraska Kansas Massachusetts Pamela Five persons S-GEM
But we know that social networks are clustred Should not the distance between randomly selected individuals be long? S-GEM
? The Small-world effect S-GEM
C(p) : clustering coeff. L(p) : average path length (Watts and Strogatz, Nature 393, 440 (1998)) Watts-Strogatz Model (from &
Ongoing Reserch and Verbal preliminary results S-GEM
Swedish Smallpox Model S-GEM
Take Home messages Variation in number of contacts Assortative interaction Clustering/Transitivity Small World Network S-GEM