Population structure in the simulation tool 4Flu
Overview
4Flu is an individual-based tool for the simulation of seasonal influenza. Up to 1,000,000 individuals are connected by a contact network which dynamically changes over age.Demographic turnover
Demographic data for 30 countries have been implemented, using official data sources. Each dataset contains the number of individuals by year of age for the calendar years 1992 to 2060. The individuals simulated in 4Flu are aligned with these age-distributions. Individuals continuously grow older and "newborns" are continuously created during the simulation year. If the size of a cohort decreases from one year to the next, a random selection of individuals of this cohort are chosen and are removed ("death") during the simulation year. If the size of a cohort increases from one year to the next, some individuals are created in this cohort ("immigration") during the simulation year.Risk status
As the vaccination coverage can depend on the risk status of the individuals, each individual also is given a risk status (either "low risk" or "high risk"). On the user interface, the user can set the percentages of newborns, 0-15 year olds, 16-59 year olds and 60+ year olds who belong to the "high risk" category. As individuals age, their risk status will be adjusted to keep the status population synchronized with these values at any time.Contact network




As individuals age, the age-distribution of their contacts also needs to change (according to the Polymod matrices). Thus, some of their contacts must be removed, new ones must be added. This is being done throughout the simulation to keep the contact network synchronized with the Polymod contact structure at any time.