SARS-CoV-2 Modelling

Ivan Perez Avellaneda, Ph.D.

November 28th, 2025

Modelling the spread of the coronavirus SARS-CoV-2

Notes on Module 1: Supply Chains, Demand Management and Forecasting

The Rijksinstituut voor Volksgezondheid en Milieu (RIVM) models the spread of SARS-CoV-2 using data to estimate the outbreak and analyse policies. We haven't yet fully understood the way the virus spreads and the conclusions drawn should be taken according to the assumptions and parameters. To acknowledge the unknowns, different options are considered in the calculations.
The reproduction number \(R\) is defined as the average number of secondary cases generated by one primary case. If \(R > 1\), the number of cases will increase, and if \(R < 1\), the number of cases will decrease. The window period is 4 days. Hospital admissions are delayed and reports of hospitalisations are submitted or updated with a delay too. Both delays are considered in the model. The estimates of R before 14 days ago are more reliable than the most recent estimates. This is the reason why today's R estimates are not reliable. Data source used to calculate R:

• National Intensive Care Evaluation (NICE) for hospital admissions.
• Municipal Public Health authorities (GGD) for positive tests in the OSIRIS system.

This includes the number of new patients, their first day of illness, the possible source of infection, and the number of people admitted to hospital. The reproduction number \(R\) indicates the ratio between the number of infections at two points in time, at intervals of approximately 4 days. Hospital admission and ICU admissions depend on the severity of the illness and are not affected by whether many or few people get tested. If we see a change in the R based on reported positive tests that is also reflected in the R based on hospital admissions and ICU admissions, then the change is probably not due to testing behaviour, but rather that the virus is more or less widespread in the Netherlands. It takes two weeks from the time that the infections occurred until the confirmed cases are sufficiently complete. Since Oct 8th, 2020, the number of contagious people has been calculated based on hospital admission by age group and on serological data from from the second round of PIENTER Corona Study. we can assume that an infected person is contagious from 2 days before the first symptoms until 4 to 8 days after the first symptoms. IC occupancy is forecasted based on a distribution model in which the population is divided into groups of the same age, and subdivided into

• People who are susceptible to infection
• People who are infected with the coronavirus SARS-CoV-2
• People who previously had the coronavirus and are no longer susceptible to infection

The model depends on their age. The probability that two people get into contagious contact is calculated based on a survey where people report how many people they have had contact with every day. If a person is infected, their age determines their risk of developing symptoms, being hospitalised, being admitted to the ICU, and dying. Based on: Nederlands' National Institute for Public Health and the Environment Ministry of Health, Welfare and Sport