Covid-19 Propagation Simulator

Insights into the dynamics of Covid-19 propagation

 

Geographic Area

Total number of people living in the geographic area.
Countries around the world are implementing social distancing measures to keep people from mixing, and to reduce this number.

 

Covid-19

Probability that a person will become infected after exposure to someone with the disease.
Time elapsed between exposure to Covid-19 and when symptoms are first apparent.
Time taken for a full recovery (days after symptoms started).

 

Hospitalization

 

Mortality Rates

Proportion of people who die from Covid-19 among all symptomatic cases.

 

Sim

 

 

 

 

 

 

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Elapsed time
Days since beginning of the outbreak

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Symptomatic
People with Covid-19 symptoms

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Hospitalized
People admitted to hospitals
Bed occupancy rate

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Recovered
People who have recovered from the virus

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Deaths
Number of deaths from Covid-19

 

Symptomatic

Need for hospital beds

Recovered

Deaths

 

 

Variable Column Comments
Elapsed time (days since beginning of the outbreak) Time -
Covid-19 cases nC (Stock) Symptomatic + asymptomatic cases
Covid-19 cases: additions (new cases per day) jIC (Flow) Symptomatic + asymptomatic cases
Need for hospital beds nH (Stock) -
New hospital beds needed per day jCH (Flow) -
Recovered cases nR (Stock) -
Recovered cases: additions (new cases per day) jR_in (Flow) -
Deaths nD (Stock) -
Deaths: additions (new cases per day) jD_in (Flow) -

 

Model

Description
Assumptions

 

The spread of Covid-19 is simulated based on a System Dynamics (SD) model, a SIR model for instance, which has the following structure.

 

Model

 

The model (cf. source code on GitHub) consists of 6 “Nodes” (where “Stocks” accumulate) and 7 “Junctions” (circulating “Flows” between “Nodes”). Their characteristics are described in the table below.

 

Object Comments Default values
nP Node, susceptible population (virus-free). Initial value: 100,000.
jPI Junction, infection rate (people per day). Four dependencies:
(1) Susceptible population, virus-free (nP).​
(2) Average number of people an average person physically meets in a day (contact rate).​
(3) Probability that a random person within the population has the virus.​
(4) Probability that a contact between an infected and a susceptible person leads to infection (infectivity).
(2) Contact rate: 5 (arbitrary value).​
(3) (nP + α × nC) / (Total population - nD). Total population: 100,000. α is the proportion of nC that show no symptoms, 25% according to NPR.org (visited on April 5, 2020). We assume people with symptoms ((1-α) × nC) will undergo quarantine and isolation.
(4) Covid-19 infectivity: 5.8% according to dwh.at (visited on April 5, 2020).
nI Node, infectious population (incubation period, no symptoms). Initial value: 1.
jIC Junction, people (per day) with the virus for whom the incubation period is over.​ Two dependencies:
(1) Infectious population (nI).
(2) Incubation period.
(2) Time elapsed between exposure to the virus and when symptoms are first apparent, 5% according to the WHO (visited on April 5, 2020).
nC Node, people with the virus for whom the incubation period is over.​ Initial value: 0.
α is the proportion of nC that show no symptoms, 25% according to NPR.org (visited on April 5, 2020).
β is the proportion of people with symptoms ((1-α) × nC) who will recover without having to be hospitalized, 86.2% ​according to LaLibre.be (visited on April 5, 2020).
jCR Junction, people (per day) who will recover without having to be hospitalized.​ Two dependencies:
(1) (α + (1-α) × β) × nC.
(2) Recovery period.
(1) jCR accounts for (a) people who show no symptoms (α × nC), and, (b) people with symptoms who will recover without having to be hospitalized, (1-α) × nC × β.
(2) Time taken for a full recovery, 20 days after symptoms started according to the Fei Zhou et al. (visited on April 5, 2020).
jCH Junction, people (per day) requiring hospitalization.​ Two dependencies:
(1) (1-β) × (1-α) × nC.​
(2) Delay to hospitalization.​
(2) Mean delay (days) from the onset of symptoms to hospitalization, 4 days (arbitrary value).
nH Node, people in hospitals. Initial value: 0.
jH_out Junction, people (per day) leaving hospitals.​ Two dependencies:
(1) People in hospitals (nH).​
(2) Hospitalization duration.​
(2) Hospitalization duration: 10.4 (8 days if critical care is not required and 16 days if critical care is required) according to Neil Ferguson et al. (visited on April 5, 2020).
nR Node, people who have recovered from the virus. Initial value: 0.
jR_in Junction, people (per day) recovering from the virus.​ Three dependencies:
(1) People with symptoms, (1-α) × nC.​
(2) Infection fatality ratio.
(3) Recovery period.
(2) Infection fatality ratio (IFR): 0.9% according to Neil Ferguson et al. (visited on April 5, 2020). IFR takes a higher value (1.35%, arbitrary value) when hospitals are overwhelmed (no more beds available).
(3) Recovery period: 20 days after symptoms started according to the Fei Zhou et al. (visited on April 5, 2020).
nD Node, deaths from Covid-19. Initial value: 0.
jD_in Junction, people (per day) dying from the virus.​ Three dependencies:
(1) People with symptoms, (1-α) × nC.​
(2) Infection fatality ratio.
(3) Delay to death.
(3) Formula (arbitrary): delay to hospitalization + µ × hospitalization duration.
µ = 75% when hospitals are working normally.
When hospitals are overwhelmed (no more beds available), µ = 25%.

 

 

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(1) The ‘sim’ is based on a simplified model. It can produce misleading or wrong results.

(2) This page describes our policy when it comes to the collection, processing and storage of our visitors’ information.

 

 

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