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Our World in Data provides a detailed and helpful explanation of how to understand deaths caused by disease. It tries to help us understand what seems like a simple question…
If someone is infected, how likely are they to die? Or put differently, what is the risk of death?
It is important to understand the difference between:
- Fatality Rate (FR)
- Case Fatality Rate (CFR)
- Crude Mortality Rate (CMR)
- Infection Fatality Rate (IFR)
Fatality Rate (FR)
One must remember that fatality rates vary greatly between age groups, ethnicities, countries, amongst people with differing medical histories and over time. This is especially important when comparing fatality rates between diseases.
This is the rate most often talked about in the media. It is:
CFR = Number of confirmed deaths from the disease / Number of diagnosed cases of disease
This is the risk a person has of dying if they know they become infected. However with diseases where many people can be infected but not know it, this rate does not answer the opening question.
The crude mortality rate (CMR)
This rate is often confused with the case fatality rate.
CMR = Number of confirmed deaths from the disease / Total Population
This number is always much smaller than the CFR because most people do not become infected. This is probably the best way of measuring the risk the average person has of dying from the disease. But this is not the answer to the opening question.
The infection fatality rate (IFR)
This is the rate we need to know to determine how likely a person will die if they get the disease.
IFR = Number of confirmed deaths from the disease / Number of diagnose AND undiagnosed cases of disease
It is the undiagnosed cases that make this rate very hard to determine. Usually this rate is lower, sometimes substantially lower, than the Case Fatality Rate. Researchers have to make educated guesses to determine this value.
COVID Rates
The Case Fatality Rate for COVID is between 1% and 3%
COVID Case Fatality rate compared to other diseases
If a person contacts the COVID virus, they are 20 to 30 times more likely to die from it than the flu.
It is possible that COVID is also spread 2 or 3 times more easily than the common flu. And the number of people who have had the annual flu shot providing additional protection is often well over 50%.
It is these three factors that make COVID a significant greater risk to public health than the seasonal flu.
More details here.
