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Mathematical model useful in pandemic planning

Illustration of Corona virus.
The new study could be useful for future pandemics. ILLUSTRATION: UNSPLASH

Using a mathematical model, researchers have been able to link confirmed covid-19 cases with intensive care admissions and deaths. The model, which allows prediction and planning of health care burden, could be valuable during the current pandemic as well as in future epidemics.

A Swedish research team, including Lund University, has used a so-called FIR model (a type of filter for digital systems) to study the last 20 months of Covid statistics. Usually, the statistics are presented as separate data with confirmed cases, the number of deaths and number of admissions for intensive care. But in the new study, published in Scientific Reports, the researchers have found that the curves coincide when the numbers are multiplied by certain factors and shifted in time.

This study gives the public a better picture of the pandemic’s course in Sweden.

“Our study provides a clear picture of the pandemic’s evolution. This very simple model makes it possible to estimate mortality and how it is affected by the vaccination programme”, says Andreas Wacker, Professor of Mathematical Physics and Principal investigator at NanoLund.

Can be used in the future

Understanding the progress of a virus during an epidemic at an early stage is of utmost importance when it comes to infection control measures and healthcare planning. The new study shows that even limited randomized testing – testing a certain number of randomly selected citizens from time to time – can provide a good estimate of the infection status and about two weeks' prediction of health care needs. The model also provides an understanding of the dynamics between restrictions, vaccination, health care burden and deaths. The study, conducted in a broad collaboration between researchers from different disciplines, is not only applicable to the corona pandemic.

“It can be used to make similar estimates for future epidemics. I was surprised that such a simple model could describe historical data”, says Kristian Soltesz, senior lecturer at the Faculty of Engineering, LTH.

Mortality fell rapidly

The study shows that an estimated 360,000 Swedish covid cases are missing from the statistics due to insufficient testing from March to June 2020. The researchers can also show how mortality changed during the different phases of the pandemic. In 2020, it was 0.8 per cent but dropped rapidly to 0.1 per cent in the first half of 2021 – a clear result of the vaccination programme. From July 2021, the mortality rate increased again, peaking in September, indicating that immunity from vaccination is declining over time. Researchers can also conclude that the number of people infected in 2020 was 1.3 million, indicating that Sweden was far from herd immunity.

“This study gives the public a better picture of the pandemic’s course in Sweden. The benefits of the vaccination programme can also be clearly seen”, says Andreas Wacker.

In addition to Lund University, Chalmers University of Technology, University of Gothenburg and Linköping University have participated in the work.

The article is published in the scientific journal Scientific Reports: “Estimating the SARS-CoV-2 infected population fraction and the infection-to-fatality ratio: a data-driven case study based on Swedish time series data”