The news, including social media, often includes more opinion than truth. This makes it hard for people to accurately understand the benefits of vaccination and how the pandemic is evolving. Today, it is very important to understand how vaccination impacts the risks of serious illness and death from COVID-19. We know that death rates can change over time as new variants of the virus appear and the effectiveness of vaccines wanes in the following months (requiring booster shots).
Here is a theoretical example:
- For a population of 60 people, we learn that 10 people died, of whom 50% were vaccinated.
- A newspaper publishes the headline: “Half of those who died from the virus were vaccinated.” This headline does not tell us anything about whether the vaccine is protecting people or not.
- To be able to come to a conclusion about this information, we would also need to know about those who did not die. For example: how many people in this population were vaccinated? How many were not vaccinated?
- To calculate the death rates, we find out that, of 10 unvaccinated people, 5 died. This means that the death rate among the unvaccinated is 50%.
- We also learn that, of 50 vaccinated people, 5 people died. This means the death rate among the vaccinated is 10%.
Therefore, we see that the death rate among the vaccinated is 5-times lower than the unvaccinated.
It is very important to compare the rates of death between vaccinated and unvaccinated people. This helps us understand misleading headlines. Comparing the absolute numbers is making a mistake. This is known in statistics as a ‘base rate fallacy,’ and it ignores the fact that one group is much larger than the other. It is important to avoid this mistake as the number of people who are vaccinated against COVID-19 is much larger than the number of people who are unvaccinated.