Case Fatality Rate vs. Infection Fatality Rate In COVID-19: It Matters A Lot

The Methods Man ^ | 07/29/2020 | F. Perry Wilson

[SeekAndFind]

As of this recording, there have been 4.2 million confirmed cases of coronavirus in the US, and 147,000 deaths, for a case-fatality rate of 3.5%.

If you were to rank the countries of the world with respect to case fatality rate you’d find the US doing ok – about on par with Germany, and Brazil. Way better than Italy, and worse than New Zealand and Australia, for instance. This is not to say we are containing the virus well, just that among those who get it, the chance of survival is about as good here as those other countries.

But there are two big problems with the case-fatality rate metric, problems this paper, appearing in PLOS Medicine, attempts to solve.

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The first problem gets talked about a lot. The case fatality rate is defined as the number of deaths from COVID-19 divided by the number of cases of COVID-19.

If you assume we aren’t capturing all the cases of COVID-19, and at this point the evidence is overwhelming that we are missing a large proportion of cases, then the case fatality rate becomes really dependent on the denominator – how many people you can test.

We tend to test those who are symptomatic, for example. And even among those with symptoms, those with WORSE symptoms – the type that might land you in the hospital – are more likely to get tested than those with less severe symptoms.

But the second problem with case fatality rate is more insidious – and it has to do with the lag between cases and deaths.

Let’s conduct a completely unethical experiment in our minds.  Take 100 healthy individuals, isolate them on a desert island and infect them all with SARS-CoV-2 on day 1.

What is the case-fatality rate on day 2 on that island?  It’s probably 0.  No one has even developed symptoms yet, much less died.

But, over time, as people get sick and die, the rate climbs – until it flattens out at some final number once everyone is either over the disease or dead from it.

If you captured everyone with the disease (asymptomatic or not) and waited until the whole thing was over to count how many people died from it, you would have the infection fatality rate.

So – case fatality rate – dependent on testing, restricted to a moment in time. Infection fatality rate – the thing we really want to know to tell how good we are at treating people with COVID-19.

The PLOS paper uses a standard susceptible-exposed-infectious-resolved model of epidemic transmission to try to turn case fatality rates into infection fatality rates. It’s an impressive bit of statistical rejiggering that basically uses the characteristics of the observed infections to model what went undetected.

For example, the case-fatality rate in Lombardy Italy, was a dizzying 17.8%. Looking at that figure alone, compared to the global case fatality rate of around 4% we might think the Lombardy was a disaster zone.

And, of course, it was to some extent – we know there was rationing of ventilators for instance – but it probably wasn’t this bad.  Using estimates from the SEIR model, the researchers pegged the infection fatality rate in Lombardy at just 1.4%. 

If the transformation is accurate – this is a much more useful metric to compare quality of medical care in different places, because countries can’t “game the system” by testing more. It can also show us how an individual country is improving in managing these cases over time. Here is the temporal trend in infection fatality rate from Hubei, China – for example.

You can see that while the case-fatality rate was rising (due to that right-censoring problem – deaths were catching up with the initial explosion of the epidemic), the infection fatality rate was falling – evidence that the docs there were getting a bit better at treating COVID-19.

When you compare countries by infection fatality rate instead of case-fatality rate, there is still variation, but it’s not the 4-5 fold difference in death rates you may have heard about.

The authors also do us a service by translating the infection fatality rate across age groups. Here the data is fairly concerning – showing 10-30% mortality – call it “true mortality” if you want – among those 70 years and older.

Now, this may be driven a bit by one of their statistical assumptions – that the ascertainment of cases is much better among older adults than younger people, considering they are more likely to be symptomatic and / or likely to get tested.  In other words, they sort of assume we’re capturing most of the COVID-19 cases in elderly people already, so the infection fatality rate and the case fatality rate are pretty close.  I’m not sure this assumption is totally valid, but it is what it is.

The authors didn’t look at US data in this study, unfortunately, so I can’t tell you how we stack up against the rest of the world using this better metric.

What I can tell you is that the CDC now provides an “infection fatality rate” parameter in it’s planning scenarios.

They range the IFR from 0.5% in their best-case scenario to 0.8% in the worst-case scenario. Given that the calculations of IFR in this study range from 0.5% to 2.5%, we may need to revise our worst-case estimates upwards.

The truth is we probably won’t know the IFR until this is all over. By then it may not be that helpful. But remember, whatever that true rate is, the total deaths will be lower if we can keep more people from being infected.

This commentary first appeared on medscape.com.

[SeekAndFind]

This article is 8 months old as I post this today, but the methodology presented here still applies.

[BenLurkin]

COVID didn’t crush the economy. Government did.

[Presbyterian Reporter]

The CFR continued to decline from the 3.5% level on July 20, 2020 until January 20, 2021 when the CFR reached 1.66%.

Since January 20, 2021 the CFR has increased and as of yesterday the CFR was 1.82%.

It is my assumption that the number of covid cases were not scaring people enough, so the Biden administration immediately went to work on new methods to increase the number of covid deaths.

[Diana in Wisconsin]

The deaths from this ‘flu’ in Wisconsin have been 0.011% of confirmed cases.

Wisconsin: 635,000 cases and 7,180 deaths, or 0.011%.

In my County (Iowa), 2,000 cases, 11 deaths, or 0.005%. Five Thousandths of ONE percent!

WHY are we still all locked up? Why HAVE we been locked up for a YEAR, now?

Oh, that’s right! Socialist Democrats! *SPIT*

What a sham.

[DugwayDuke]

Thank you for the very good article.
It highlights one of the major problems with this pandemic, the lack of good information. Lacking that information, our health care professionals went worse case panicking our politicians and the public.

the really interesting reads will be the after action reports published in three/four years.

[rktman]

Actual CV19 fatalities or “reported” CV19 fatalities. THAT makes a difference. But that will probably never see the light of day.

[Cobra64]

What a bunch of useless crap. Even the CDC admits the numbers are BS, yet pearl-clutching morons eat this stuff up.

[Cobra64]

Traffic deaths and natural causes are included in the Covid death numbers. A lot of people believe in the Easter Bunny and the tooth fairy too.

[Mr. Jeeves]

It highlights one of the major problems with this pandemic, the lack of good information. Lacking that information, our health care professionals went worse case panicking our politicians and the public.

False information is used to make policy - which is not subsequently changed when correct information surfaces.

Meaning the policy was pre-planned and the false information was just a pretext to implement it.

[SeekAndFind]

RE: Actual CV19 fatalities or “reported” CV19 fatalities.

I assume that the “reported” fatalities are larger than the Actual fatalities, but by how much? Anybody have a reasonable estimate?

[rktman]

That would take a lot of digging and research which I’m guessing ain’t gonna happen. Applecart upset.

[Bonemaker]

“..the really interesting reads will be the after action reports published in three/four years...”

The democrats will probably unleash 2 or 3 new pandemics during that time span.

[bateau]

Your math is wrong. You are not converting to percentage correctly. After dividing numerator by denominator, you have to move the decimal point to the right 2 places for it to be reported as percentage.

[RC one]

Case fatality rate is a snapshot in time that encompasses various factors. It can change from one day to the next but, more to the point I'm about to make, it can be changed, from one day to the next; for example:

Take a hospital that's operating at 50% of its operational capacity and then flood it with 100 acutely ill patients suffering from a highly contagious, potentially deadly and not well understood virus. That's a bad scenario. Let's say 25 of those people die. That's a 25% CFR.

Take that same hospital a week later when it's operating at 105% of its operational capacity. It's still more than filled with these acutely ill patients. Staff is getting sick and so everyone is having to carry extra water. Now hit that hospital with another wave of 100 patients suffering from this highly contagious, confirmed to be deadly and still not well understood virus.

Do you think the CFR will still be 25%? No way. You'll end up with a 50% CFR this time and by that time, the entire hospital will be on the verge of anarchy and collapse like we saw in NYC.

I mention this because this is why we stressed the need to "flatten the curve" early on, to prevent this kind of a scenario from developing. The logic seemed to be lost to many.

[Widget Jr]

Bookmarked, a good article and video.

It shows the problem in getting good information on new diseases. Getting reliable information in medicine takes time. The flue has been around for over 100 years old. Covid-19 is 15 to 18 months old. That is a huge difference. We simply do not have the information on Covid-19 like other diseases.

[ConservativeInPA]

A lot of people believe in the Easter Bunny and the tooth fairy too.

Personally, I believe in the Easter Bunny and Tooth Fairy a lot more than anyone in government. Now that Santa Claus guy, he obviously works for the government - handing out all that free stuff.

[ransomnote]

What would the fatality rate be if the CDC did not do everything it could to withhold treatment?
Patients weren’t even allowed a “right to try” HCQ. All treatments were denied until the patient was hospitalized and put on excessively aggressive ventilator therapy, which injured infected lung tissue.
What would the fatality rate be if doctors were simply allowed to prescribe medicines they deemed fit for their patients? What would it be if the CDC didn’t recommend such aggressive respiratory therapy.
And then - what if 5 governors didn’t force Covid-19 patients into nursing homes. Early in the planned-demic, nursing home deaths accounted for 40% of fatalities?

What if the CDC didn’t require deaths to be counted as Covid-19 based on stupid, statistic distorting rules? If you died within 60 days of having a positive Covid test then it counts as a Covid death! Keep in mind the inventor of the Covid-19 test they use (PCR) said it was NOT appropriate for use for the planned-demic because it would result in MANY false positives.

So people with false postives, and people with actual positive covid test die a month later in a car accident and it’s a Covid death. At that press conference, the example was a ‘motor cycle accident’ and the speaker said, yes it would be counted as covid but advised the public to remember that such accidents would be statistically low and have little effect on overall fatality rates.

Coroners and physicians reported struggling with the instructions that when their patients died with multiple co-morbidities, they were to record the death as Covid. So someone dying of cancer with a positive Covid test, even without symptoms, would be recorded as Covid. The example I watched in a video was a doctor frustrated with ‘new rules’ for Covid which meant his patient with failing health, COPD, Diabetes, Kidney failure etc. would ‘have’ to be recorded as Covid death.

The planned-demic is all lies. All of it.

[Diana in Wisconsin]

Thanks, Perfesser! ;)

[Chauncey Gardiner]

The only metrics that matter are - # hospitalizations and # morbidities. The rest are coffee table fodder.

[Jane Long]

Amen and BTTT.

Hubby and I were just talking about a lot of your points made, this morning.

It’s been a year since friends of ours contracted China Flu.

They’re young, healthy and fought it off, with barely any down time. They both receovered, completely, and TO THIS DAY are still cranking out antibodies.

Now....imagine if there had been NO lockdowns and people were told what precautions to take, to prevent....AND....given early access to KNOWN, safe preventatives, early on safe and EFFECTIVE TREATMENTS, should they HAVE contracted this bioweapon virus.

Meanwhile, people could’ve gone about their day to day business, as usual, or as THEY chose.....herd immunity would’ve been reached LONG ago, deaths of our elderly and/or those with comorbidities PREVENTED, for the most part....and...they wouldn’t have had anything to blame on Trump, except more winning.