Covid 19 - Contacts

Problem definition

The global Covid 19 pandemic is impacting everyone's lives. To contain the pandemic, mass events have been banned in Germany since 2020 and masks must be worn daily on public transport and in stores. These measures are increasingly criticized and disregarded by some parts of the population.

This simulation is used to illustrate the impact of bans on mass gatherings on infection rates and the extent to which wearing masks protects all members of society.

Method

NetLogo is used for the simulation. This allows the representation of autonomous agents.Thus, pandemic behavior can be well represented in a situation where people/agents move differently in the daily routine. Hence, reality can be suitably represented in an abstracted model to show the specifics of a pandemic spread.

Model

The model shows the abstracted version of a village. The houses of the inhabitants and points of interest (office, shops...) are randomly distributed through the village. The model simulates the daily routine of the inhabitants. The day is determined by a fixed number of ticks. At the start of a day the inhabitants are in their permanently assigned houses. Around 8 a.m. all residents leave their houses and go to one of the different points of interest. In the afternoon, residents return to their homes.

In this village, the spread of Covid 19 is simulated. Residents can become infected by being close enough to infected residents for a sufficient amount of time. If the contact is long and close enough for an infection, the person turns orange. If an infection has occurred, the chain of infection is represented by a link The person now infected also become contagious after an incubation period, turns red, and can infect other persons at home, on routes, or at one of the points of interest. Infection lasts between 7 and 10 days, after which time the person may die from the infection (triangle) or become immune and turn purple.

World

The world consists of a 64x64 patches standard Netlogo world. We assume one day as 240 ticks.

Static Elements of the World

At the beginning of each run the world is filled with its static elements, namely the points of interest and houses, each of which takes a random position. Houses are permanently assigned to agents. The number of houses is a quarter of the number of people to be generated, which is set at the start. A group of agents assigned to a house is called a family. One family lives per house.

Points of interest (pois) are stores, offices, schools etc. Which will be repeatedly visited by groups of people.

Dynamic Elements of the world

In the following, a given number of inhabitants is generated. When generated each person is assigned a random home (one-of houses) and a random point of interest (one-of pois). All people follow the same day structure: at around 8 am (80 ticks) each person decides with a given probability (home-prob) if he stays at home at this day. If he decides to leave the house he goes to his assigned point of interest with a given probability (1-pois-var-prob) or goes to a random point of interest. After eight hours (80 ticks) each person heads back home where he stays till the next morning.

Covid 19 Infection Mechanism

At the start a fixed number of infected and contagious people is given. The infection is indicated by setting the color of the person to red. For each healthy person is checked in each tick if there are any contagious persons within a certain radius. If infected persons remain within this radius for a sufficient time, the healthy person can become infected with a certain probability (inf-prob) per tick. If a person is infected he enters the incubation period indicated by changing its color to orange. After infection, a directed link is drawn from a randomly selected infected person present within the radius to the infected person. The incubation period length is derived from the log-normal distribution for each person. At the end of the incubation period the person becomes contagious for a given amount of time, derived from a moral distribution. After which the person recovers and becomes dies or becomes immune with a given probability. Death is indicated by a triangle. Immunity is indicated by a purple color.

Parameter

We differentiate between three types of parameters. The world parameters which describe the given situation in the village (number of people, number of pois, ...). Secondly, the behavioral parameters which determine the actions of the people and can be influenced by the anti-pandemic measures. And finally, infection mechanic parameters which describe how long a person is contagious. The parameters of the first two groups can be adjusted using sliders. The last group of infection mechanic parameters is derived from scientific findings about the Covid 19 pandemic.

World Parameters

persons - initial number of inhabitants of the village infected-int - initial number of infected and already contagious people cnt-pois - initial number of points of interest

Behavioral Parameters

inf-prob - the probability of infection per tick for healthy people surrounded by contagious people after a given time and can be influenced by ant-pandemic measures as wearing masks, banning mass events and reducing contacts home-prob - the probability of a person of staying home and not leaving in the morning to any point of interest pois-var-prob - the probability of a person to go to random point of interest instead of the one initially assigned (simulates shopping, meeting other people, staying at other points of the village, ...)

Infection Mechanic Parameters

Initially the Inf-prob is set to 0,01 - because of given R wert

Results

Beispiel mit wenigen Personen um Infektionskette genau verfolgen zu können