Covid-19 should not be compared to seasonal Influenza
It’s normal to look at the CFR (case fatality rate) of seasonal influenza when considering Covid-19. After all, 20-45 million get “the flu” every year. The numbers vary depending on the year. The “low” was the 2011-2012 season with 9.3 million cases and 12,000 deaths and the high was the 2017-2018 season with 45 million cases and 61,000 deaths.1
Let us look at the worst of eight recent flu seasons. The CFR for that was 0.0014 meaning, 1.4 persons died per 1000 cases. Interestingly, if we look at the “best” of the past eight seasons (the “good” one) the CFR is 0.0013, almost the same number of deaths per thousand cases.
So, hold on to this thought...
Seasonal influenza’s average risk of dying is about one death per 750 cases.
I see and hear CFR for the Covid-19 repeatedly being quoted at around 2-3%. CFR currently (as of 2/27 12:23AM EST) is 3.4%. That is 2,810 deaths divided by 82,550 cases.
But to say that the CFR for Covid-19 is 3.4% is not wise. Why? Simply put, the CFR is not applicable are even a number that one can calculate since it's a "look-back" number.
For data current as of 2/27, click here.
CFR is a “look-back” rate
It is very useful when we look back to an epidemic/pandemic that has ended. For instance, when comparing the “good” 2011-2012 flu season to this season’s numbers. CFR is death rate / # of confirmed cases. To divide the known number of cases today by the number of deaths, we get 3.4%. But this is not wise to use because it assumes that ALL of the remaining cases (total cases today of 82,550, minus cases where the person has recovered or died) will be cured. This is “magical thinking.” Many of those remaining 46,488 will recover, but some will die.
In short, we won’t know the true CFR for another year or more. CFR is useless at this time, it will be helpful sometime next year.
Known outcomes
So, let us look at the cases with known outcomes, meaning the sum of the cases of those who have recovered plus those who have died. This population is composed of those 33,252 who have, to today, recovered plus the 2,810 who have died; thus, our population is 36,062. If we divide 2,810 (deaths) into our population of 33,252, we find an overall death rate of 8.45% or about 85 per one thousand cases with known outcome.
Please let that sink in for a bit. Today, looking at Covid-19 cases with known outcomes, 85 out of 1000 cases have died.
Should this hold, and it may, then 1 out of 12 cases will die.
Compare this to seasonal influenza where 1 out of 750 cases will die.
The death rate currently for Covid-19 is 62x the death rate of the average seasonal influenza.
These two illnesses do not compare, although we’ll really not know for a year or so, at which time we can look back to see what the true CFR rate was.
Let us look now at areas/countries to see the current death rate is, of those cases with known outcomes.
I’ll call the current fatality rate of known outcome cases: CFR-KO.
I shall call the population with known outcomes: PWKO
Total deaths / PWKO = CFR-KO or current death rate.
World: 2801 / 36,062 = 8.45% or ~85 deaths per 1000 cases.
Hubei Province: 2641 / 26,024 = 10% or ~100 deaths per 1000 cases.
South Korea: 13/35 = ~37.2% or 372 deaths per 1000 cases.
Italy: 14/54 = ~26% or 260 deaths per 1000 cases.
We see that regional epidemic outbreaks tend to drop in CFR-KO as time goes by. Whether the true “look-back” CFR will drop to 2 or 3% or some other number (lesser or higher) depends on many factors which are simply unknown. For instance, children appear to be much less at risk for Covid-19, and cases within Africa (other than the one in Egypt) seem oddly absent. Perhaps the virus does not do well in warmer climates. Perhaps the fatality rate will drop as we approach Summer in the Northern hemisphere—we do not know.
Perhaps the tendency of the media to quote the 2-3% theoretical CFR comes from the fairly recent 2009 H1N1 flu pandemic. The 2009 “swine” flu was very feared. It infected 10-200 million world-wide with estimates of death ranging from 105,700 to 395,600 and a CFR of 0.03% or 3%. (30 per 1,000 cases). (Wikipedia). It was expected to return far, far worse numbers.
The “swine” flu, which was the first pandemic of this century, turned out to be far less lethal than many expected. Triggle wrote in an article from December 10, 2009 titled, Swine flu less lethal than feared, "The swine flu pandemic is ‘considerably less lethal’ than feared, chief medical officer Sir Liam Donaldson says,” adding, “A study led by Sir Liam found a death rate of just 0.026% in those infected, the British Medical Journal reported.”2
Will we be lucky?
Perhaps we’ll be lucky this time, too, although I suspect we won’t be as lucky as we were for the “swine flu.”