Overview of the simulation tool 4Flu


4Flu is a freely available, highly sophisticated individual-based tool for the simulation of seasonal influenza which allows to compare vaccination strategies. It has originally been developed by Epimos GmbH (Epimos) for GlaxoSmithKline GmbH & Co. KG (GSK), but now has been made available for the public free of charge to foster the discussion among experts. Software design and programming of 4Flu were done by ExploSYS GmbH.

System requriements

4Flu is written in JAVA. It runs on various operating systems (Windows, Macintosh OS X, Linux). Java version 1.7 or newer must be installed. In case of problems, please consult the FAQ.

General features

Splash screen of 4Flu 4Flu simulates the spread of the four influenza strains A(H1N1), A(H3N2), B/Yamagata and B/Victoria in a population of up to 1 million individuals. Being an individual-based simulation tool, it makes ample use of random numbers. Because of this, each simulation run can be different, and the results of many simulations should be averaged before drawing conclusions.

Some of the features of 4Flu are:
  • Realistic age-structures for 30 countries.
  • Up to 1,000,000 individuals are connected by a contact network which dynamically changes as individuals grow older.
  • Choice of 8 different contact networks (derived from Polymod study).
  • Simulation are initialized for 20 years before the evaluation period begins, which also runs for 20 years.
  • Seasonal transmission of influenza; independent transmission of 4 strains.
  • Natural history influenza:
    • Latent period.
    • Infectious period depends on age.
  • Highly sophisticated immunity model, including
    • Gradual loss of immunity.
    • Boosting of immunity by infection or vaccination.
    • B lineage cross protection.
    • Immunity loss due to new drift variants.
    • Unspecific protection after infection.
  • Highly customizeable vaccination model, including
    • Choice of either trivalent or tetravalent vaccine.
    • Choice of vaccination coverage by age and risk group of individuals.
    • Simultaneous comparison of two different vaccination strategies.
    • Possibility of vaccine mismatch against new drift variants.

User interface

4Flu comes with a user interface which allows the user to change nearly all simulation parameters. The user can explore different scenarios and save interesting parameter constellations to a file which can later be loaded to re-run these simulations. While the simulation runs, summary curves and tables are displayed and continuously updated on the user interface.

User interface of 4Flu


4Flu output is displayed in curves and also given in tables; it includes:
  • Weekly incidence of infections (by vaccination strategy, influenza variant, and by age groups)
  • Cumulative number of infections (by vaccination strategy, influenza variant, and by age groups)
  • Cumulative number of vaccinations (by vaccination strategy, and by age groups)
  • Immunity status of the population (by vaccination strategy, influenza variant, and by age groups)
  • Size of the population (by age groups)
  • Composition of trivalent vaccine (by year), occurrence of drift variants, and vaccine mismatch.
  • Excel export for summarized simulation output.