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Comment by nednar | Hacker News Reader

Side question:

The very first comparison of covid-19 and seasonal flu I read (before covid-19 was called covid-19) said that covid-19 would have a mortality rate of 1.5% and seasonal flu of 3%, therefore covid-19 would be less deadly. In recent months I often read the same statement turned around, which is already confusing. Now here we talk about a tenth of the same numbers turned around.

I mean, either it's not standardized what "mortality rate" means or the numbers are all over the place and one can't really say which is more deadly.

Could someone with more knowledge in this area summarize the current status and maybe where the confusions might come from?

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It's the difference between IFR and CFR. The IFR is the infection fatality rate meaning everyone in the population who has been infected. The CFR is the case fatality rate, those who are sick enough to show up at a hospital, or well, get tested and confirmed positive. Which nowadays is essentially the same and a small fraction of total cases.

We see here that flu seems to have an overall IFR rate of 0.002%. Many orders of magnitude smaller than COVID19.

https://www.cdc.gov/nchs/fastats/flu.htm

Where do you get IFR for covid19?

The IFR rate for covid-19 seems to be trending towards 0.1-0.5% based on the serological tests over entire population cohorts that are starting to be published.

I thought it was between 0.5% to 1.0%, at least according to the NYC study: https://twitter.com/trvrb/status/1253436656742305793

By doing serologic studies you can estimate the global number of contaminated people: looking at the number of viral mutations, as well as different strands of the virus that can be identified as being generated in a specific region.

It’s going to be very imprecise. For H1N1 the global infection rate could have varied from 11% to 21% of the global population, which is a +/- 350 million people estimation.

https://www.cidrap.umn.edu/news-perspective/2011/08/study-pu...

0.002% is again a different number than 3%, 1.5%, 0.3% and 0.15%.

Also to compare two numbers don't you need a second one as well? 0.00002 is a magnitute smaller than what number?

The IFR rate for covid-19 seems to be trending towards 0.1-0.5% based on the serological tests over entire population cohorts that are starting to be published.

According to the CDC, the seasonal flu kills 12,000-79,000 Americans a year by the same standard as used for COVID-19. Much closer to the widely cited 0.1% IFR.

https://www.cdc.gov/flu/about/burden/faq.htm

Seems high. Here is a systemic review of studies done on the 2009 influenza coming to a conclusion of an IFR of 1-10 deaths per 100 000 infections.

"The consistent estimates of the infection fatality risk at around 1 to 10 deaths per 100,000 infections identified in our review"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3809029/

CEBM concurs, the H1N1 CFR was between 0.1% and 5.1%, based on country and the fatality risk settled out at 0.02%. [1]

Some more napkin math, the CDC estimates between 12,000 and 61,000 flu fatalities per year out of approximately 9,300,000 to 45,000,000 infections so pretty consistently a 0.1-0.15% IFR. [2]

Not sure how to reconcile these. The worst year, 2017-2018, had 45M cases and 61K deaths. The dominant strain was H3N2 not H1N1. The vaccine wasn't particularly effective that year (38%). Not sure how else to account for the delta. [3, 4]

[1] https://www.cebm.net/covid-19/global-covid-19-case-fatality-...

[2] https://www.cdc.gov/flu/about/burden/index.html

[3] https://www.cdc.gov/flu/about/burden/2017-2018.htm

[4] https://www.cdc.gov/flu/vaccines-work/effectiveness-studies....

> Deaths per 100,000 population: 2.0

Your 0.002% number is the POPULATION Fatality Rate not the Infection Fatality Rate (IFR).

If someone said the flu has a 3% ifr (infection fatality rate) they were way off.

The best guess for the covid-19 IFR I've seen is ~1%. New York City has has .02% of it population die above the base death(excess deaths). And the last serological study said 20% of people have been infected. So that gives us an approximation of 1%.

This is 10x-100x worse than the flu.

> New York City has has .02% of it population die above the base death(excess deaths)

Where did you get that number? The numbers I’ve seen are several orders of magnitude higher.

2% (2 orders of magnitude above 0.02%) of 8 million (approximately the population of NYC) is 160,000 people. So that's clearly wrong being more than 3 times the entire US deaths.

The numbers you've seen are probably deaths of infected people not the entire population.

> The numbers you've seen are probably deaths of infected people not the entire population.

No, I just slightly misread OP’s confusingly worded stat. Base deaths in NYC is around 6k/month. Covid-19 deaths alone have been way above that number. Numbers are obviously not in for the month of April yet, but it’s looking more like it’ll be closer to 30k deaths in NYC per CDC[0]. So that’s 24k more deaths per month, aka 5x (where my several orders of magnitude came from). If you use the scale OP used, that’s about .3% of NYC population in excess deaths, so one order of magnitude higher.

[0] it’s at 26k right now with a bit under a week left - https://www.cdc.gov/nchs/nvss/vsrr/covid19/index.htm

Excess deaths in New York City: 19,200.

Population of New York City: 8.4 million.

19,200 / 8.4 million 0.22% dead.

20% infection rate = IFR of ~1.1%

https://www.nytimes.com/interactive/2020/04/21/world/coronav...

Yes, I know those numbers. That’s not what OP said that I was responding too (see reply to sibling comment for more context).

One thing that didn’t seem to be noted in the rest of the comments: the actual mortality rate can’t be formally calculated until the pandemic has subsided. What you are seeing now are estimates and projections for the number that they’ll end up being able to calculate when the disease has stopped spreading.

Remember that IFR of a disease alone does not tell you how many people ultimately die from it. The R0 number, which determines how quickly the diseases spread, determines total cases and then cases X IFR = deaths.

My understanding is that Covid-19 has a much higher R0 than the seasonal flu.

Maybe loose terminology so ending up getting case fatality rate confused with mortality rate?

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