COVID-19: CFR vs IFR
Published September 13th, 2020 under Editorial
A Case Fatality Rate (CFR) is defined as the proportion of deaths among confirmed cases of the disease … while an Infection Fatality Rate (IFR) is defined as the proportion of deaths relative to the prevalence of infections within a population. – Dr Ronald B. Brown1
In late January, I was reading online about the death rate of the novel coronavirus (later named COVID-19). The mass media and the WHO (World Health Organisation) were reporting scarily high death rates. I had seen these sorts of grossly inflated numbers during the 2009 pandemic, and so knew to be very cautious of them. On reading the report direct from the WHO, it was very clear that these were only a measure of the CFR (Case Fatality Rate) rather than the IFR (Infection Fatality Rate). However the WHO were directly comparing this data in their own reports to the IFR (Infection Fatality Rate).
Globally, about 3.4% of reported COVID-19 cases have died. By comparison, seasonal flu generally kills far fewer than 1% of those infected. – WHO Director General March 2020 2
Reported “death rates”
By late February/early March, almost everyone I spoke to about COVID-19 was concerned about the high “death rate” reported for COVID-19. Most claimed we needed to take drastic action to stop the virus. When I pointed out what those numbers actually meant, and that we did not have information yet on how they compared with “standard” diseases such as seasonal influenza, many would simply claim I was misunderstanding the situation and that the numbers reported by the WHO were “obviously correct”. But the numbers reported by the WHO were correct, they just weren’t a measure of what many they thought.
I had neither the knowledge, skills or time to estimate an IFR for COVID-19. Despite this, and based on not much more than eye-balling the raw data, I gave an extremely crude off the cuff prediction of a final infection fatality rate in Germany of 0.21% on March 23rd 2020.3
In late March 2020, a series of papers were published by UK based investigators which began to properly dig into estimations of the prevalence of COVID-19 in the community.4,5, 6 Extrapolating from their estimates of COVID-19 prevalence, combined with mortality data, gave estimates of sub 1% death rates (eg: 0.66% IFR for China). This alarmed me, as they were significantly higher than my own crude estimate.
By early April, I had become exasperated by the continued references to “death rates” in the mass media and amongst my friends. I was consistently seeing people using the current COVID-19 CFR to compare COVID-19 to the IFR of other diseases such as influenza. Directly comparing the CFR of one disease to the IFR of another disease is misleading and meaningless.
On April 9th 2020, I wrote a post on Facebook expressing my concern regarding the lack of data available regarding infection fatality rates.7 At almost the same moment, research results started arriving which validated my concerns. The first major study was the “Heinsberg study”, which was a small but very focused study on the area of Gangelt in Germany.8 They conservatively measured an IFR of 0.37%, but Professor Hendrik Streeck (lead scientist of the study) stated publicly that be believed the final IFR would more likely be “closer to 0.24 to 0.26% death rate”.9
Since then, a plethora of studies on COVID-19 infection fatality rates based on antibody studies have been published. There is now a preprint review of these studies published by Professor John Ioannidis of Stanford University, which gave an average values of 0.25% (an initial peer review report on this paper is available).10, 11.
A more consistent use of death rate in the media and public conversations would drastically aid in the understanding of the current situation and help people gain a clearer view of what the facts are. I believe that having a consistent and accurate report of the facts would reduce the confusion and conspiratorial thinking in the general populace. I hope my clarification goes some way towards that goal.
Craig Sailor for encouragement and listening to me bleeting on about this subject for months on end and Dr Mauritius Seeger who was the initial source of my frustration, but provided a useful analysis from the polar reverse point of view.
Conflicts of interest
I’m just some random dude hacking away on his keyboard. I have no beef in his game other than getting ticked off at data being misused.
This was not intended as a scientific paper. I am a scientist (or was), but my background is in synthetic chemistry and drug development; certainly not epidemiology or virology, so I am far from an expert on this subject. I didn’t even know the labels CFR and IFR before this pandemic started. I’m just upset at how data is being misrepresented and felt the need to get off my chest. It’s a subject which has frustrated me for years, but my frustration has burst forth during the COVID-19 pandemic since so many people and media outlets have been falling into the same trap.
1. Definition of CFR – https://www.cambridge.org/core/journals/disaster-medicine-and-public-health-preparedness/article/public-health-lessons-learned-from-biases-in-coronavirus-mortality-overestimation/7ACD87D8FD2237285EB667BB28DCC6E9
2. WHO Director General remarks March 2020 – https://www.who.int/dg/speeches/detail/who-director-general-s-opening-remarks-at-the-media-briefing-on-covid-19—3-march-2020
3. My COVID-19 IFR estimate – https://geek.hellyer.kiwi/predictions/
4. Estimates of COVID-19 infection rates by Imperial Colleg London – https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-Europe-estimates-and-NPI-impact-30-03-2020.pdf
5. Estimates of COVID-19 infection fatality rate – https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30243-7/fulltext?fbclid=IwAR3WHA0n7M-
6. COVID-19 estimates for European countries – https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-Europe-estimates-and-NPI-impact-30-03-2020.pdf
7. My Facebook post about COVID-19 – https://www.facebook.com/ryanhellyer/posts/10159079536591789
8. Heinsberg study – https://www.medrxiv.org/content/10.1101/2020.05.04.20090076v2
9. Interview with Professor Hendrik Streeck – https://www.youtube.com/watch?v=vrL9QKGQrWk
10. Literature review of serology studies – https://www.medrxiv.org/content/10.1101/2020.05.13.20101253v3.full.pdf
11. Peer review notes for (8) https://rapidreviewscovid19.mitpress.mit.edu/