I’ve wondered ever since the Covid-19 pandemic began in 2020 if there were any methods to predict when the pandemic might end. This question led me to discover the SIR model, a mathematical model used by scientists to predict the course of an infectious disease. But what is the SIR model? And what does it tell us about Covid-19 in BC?

**What is the SIR model? **

The SIR model was first introduced in 1927 by Kermack and Mckendrick. It consists of a set of mathematical formulas used to simulate a disease’s spread through a population. The model does this by sorting individuals into one of three compartments: susceptibles, infectious, or removed. It then uses the mathematical formulas to measure the change in each compartment over time to predict the disease’s course.

**Who counts as a Susceptible, Infectious, or Removed?**

Individuals are identified as **Susceptibles** if they have not yet become infected by the disease. **Infectious** persons are infected and can spread the disease to others. People become** Removed** when they have either recovered or died from the disease. Recovery or death means that those removed cannot contract or transmit the disease anymore.

**What about Covid-19 in BC?**

The SIR model can be applied to Covid-19 in BC to try and predict its spread. I substituted BC’s Covid-19 numbers, taken from BC’s official website and the Centers for Disease Control, into the three SIR model equations. These equations create an excel graph used to visualize the pandemic.

#### What does the SIR model about BC tell us?

This graph shows the number of people in each compartment over time in BC due to Covid-19. It predicts that the pandemic will end approximately 600 days after the initial infection. The flattening curves in the graph represent this. Additionally, it models that close to 3.3 million people will become infected during this period.

Yet, compared to real Covid-19 numbers in BC, these predictions are very large. In reality, there have only been approximately 50,000 total infections since March 2020. The SIR model’s severe overestimation is due to its inability to account for preventative measures. Measures such as social distancing and mask-wearing significantly reduce the number of people that will get infected and the duration of the pandemic. The lower Covid-19 numbers in BC compared to the SIR model’s predictions prove that the guidelines and preventative measures employed by the province are working to reduce the spread. With continued safety practices and a vaccine right around the corner, I am confident that we can defeat Covid-19 sooner rather than later.

The SIR model is a powerful mathematical tool for scientists to study the dynamics of pandemics. Although it has its limitations, it still contributes an important piece of information in the fight against the spread of infectious diseases.

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