Another number, which you you'll
hear, another estimate I should say,
is the “Case fatality rate,” which
actually should be, “Case fatality ratio.”
This this estimates the mortality ratio,
among documented cases and it's
calculated by taking the number of deaths,
divided by the number of documented cases.
As noted, we should not
really consider that a rate,
but unfortunately, rate, is the usage or the term,
which most individuals in the social and
common media and literature have used
and so, you'll hear us use rate.
Ratio of course, is the more
accurate statistical number.
This number the “CFR” is not a constant
and it's also a very poor measure,
during an epidemic.
You could pause this this session right now,
just think about reasons for that.
But of course, what you're coming to come up with,
is that, the CFR will typically
overestimate the true death rate,
why is that?
Because our denominator the total number of cases,
we don't know the number of asymptomatic cases,
we don't know the number of
true cases that were not tested
and not confirmed and so our “n” our denominator,
is likely far larger than what
we are using to calculate the CFR
and again, as we say here most death by infection
are also noted going to be noted
because they may not be diagnosed
or they may be attributed to something else
or they may be wrongly attributed to
infection with SARS-Coronavirus II,
The crude mortality rate
is a measure of the proportion
of the entire population
that die from a particular disease.
This is very different from the case
fatality rate, which only factors disease
individuals into the equation
and discounts the healthy population.
So again, perhaps a more accurate
estimate of the mortality rate,
is the infection fatality rate the “IFR.”
And this is the number of
deaths due to infections,
divided by the total number of infected people.
So, inserting here, is going
to be a better attempt,
to confirm that deaths and
infections are specifically due,
to the disease of interest, in this case COVID-19.
So, the IFR, should be a better measurement,
it will almost always be lower than the CFR,
just due to the imperfections
in calculating the CFR.
The IFR, will include both documented and
undocumented or asymptomatic cases
and it's going to be typically
estimated at the end of a pandemic.
Although of course estimates will
occur throughout the epidemic,
but it is largely looking in retrospect,
that one can accurately calculate the IFR.
Why is it more accurate?
Because it requires
documentation of the infection,
typically, through antibody studies,
the IFR is going to vary with the
distribution of other factors,
comorbidities, so age, health
issues, pre-existing health issues,
other qualities of the infected individuals,
as well as qualities of the
medical care they receive
or have access to.
So, you can imagine then that that for COVID-19,
that the, true mortality rates
have and will vary greatly,
across different countries and age groups.
The CFR currently
is being estimated at 1.2% with COVID 19.
The IFR is closer to 0.5%.
We must remember that this may be higher
in specific populations,
for example, in communities in which 20%
of the population is over 85 years of age.
The IFR may reach 4%.
Neither the CFR nor
the IFR can account for the full burden
of COVID 19 because they don't
include mortality, which is indirectly
caused by the pandemic.
An example of this would be delayed
care for other medical conditions
Perhaps the health system itself is overburdened,
certainly, we're seeing this
in many parts of the world,
were, the sheer vast numbers of COVID-19 patients,
has overwhelmed the medical
setting, clinics, hospitals,
emergency departments and there
is insufficient medication,
or healthcare personnel, ventilators, IV fluids
and thus, those who do make
it into the healthcare system,
encounter an overburden system,
which has a very decreased quality of care.
Social determinants of health,
this is a very difficult
and yet a very important factor which
will impact on both CFR and IFR.
So those individuals who lost their
jobs because of all the social closures.
Decreased social interactions,
causing perhaps mental health variabilities,
maintenance of education,
maintenance and mental health et cetera.
All these have the ability to intervene or impact
on the CFR or the IFR.
So, as an example, again in real time,
these are still estimates, but the fatality rates,
in individuals with COVID-19
who also have comorbidities
and you see them listed here.
Cardiovascular disease, the
mortality rate, the fatality rate,
over 10%, those with diabetes,
especially those with insulin
dependent diabetes, 7.3%,
those individuals with chronic
respiratory disease, 6.3%,
death rate from COVID-19,
pre-existing hypertension or other
cardiovascular disease, 6.0%,
those with cancer immunodeficiencies, almost 6.0%,
those who had no pre-existing conditions,
so zero comorbidities, age, obesity,
any other medical conditions,
that the estimate of the fatality
rate with COVID-19 is just 0.9,
while that is still much higher,
than it is for influenza,
where the estimate is 0.1%, yet that
is far less significantly horrible,
than as we see with cardiovascular disease.
So, it is through using these
statistical predictive numbers,
that we can both follow as well
as predict areas of the world,
which are going to be negatively
affected by the COVID-19 pandemic
and it is certainly the wish and the concern,
to continue to use these successfully
to drive resources and to do a
better job of impacting on COVID-19.
case fatality rates from China
in February of 2020 which show
how preexisting medical conditions
can impact the disease
So far, age has proven to be
the strongest risk factor for severe COVID
19 outcomes, including death.
The number of preexisting conditions
has also been shown to be associated
with worse outcomes.
And finally, with each new virus variant,
the symptom profile
immunogenicity and treatment
resistance of the virus
can all evolve
to result in worsening outcomes.