Thursday, November 19, 2020

Reproduction Numbers, Herd Immunity, And All That Jazz -- November 19, 2020

First, reposting this:

Chinese flu watch: at link, be sure to set filter to "yesterday" --

  • North Dakota moves up a notch, now #8 for deaths per capita
  • South Dakota also moves up, from #23 recently to #16
  • cases/per capita
    • North Dakota, #1, nearing 9% (70% or greater needed for herd immunity -- long way to go)
    • South Dakota, #2, nearing 8%
    • Iowa, #3, just over 6%
    • Texas, #25, not even at 4%; with some of the hottest spots in the US, still only #25 on this list
    • New York, #32, barely above 3%; the "city" shuts down all schools as of yesterday, November 19, 2020 -- bars, gyms, and restaurants remain open; over 300,000 students affected;

Now, go back and take a look at this post regarding production numbers:

Basic reproduction number for measles:

The basic reproduction number, R nought (R0), is defined as the average number of secondary cases of an infectious disease arising from a typical case in a totally susceptible population, and can be estimated in populations if pre-existing immunity can be accounted for in the calculation. 

R0 determines the herd immunity threshold and therefore the immunization coverage required to achieve elimination of an infectious disease

As R0 increases, higher immunization coverage is required to achieve herd immunity. In July, 2010, a panel of experts convened by WHO concluded that measles can and should be eradicated. Despite the existence of an effective vaccine, regions have had varying success in measles control, in part because measles is one of the most contagious infections.

In that second link, it was stated: 

As R0 increases, higher immunization coverage is required to achieve herd immunity.

The reverse: as the R0 decreases, the lower the immunization coverage is required to achieve herd immunity. 

Not enough folks are talking about this.

I'm getting the feeling even Dr Faust has missed this (or deliberately ignoring it). Even at 90% vaccination rate he said that we still need to wear masks and distance ourselves socially forever and ever.

From wiki and various other sources, generally-agreed-upon reproduction rate numbers:

  • measles, 12 - 18
  • chickenpox: 10 - 12
  • polio: 5 - 7
  • smallpox: 3.5 - 6
  • Chinese flu: 2- 6 (but still, probably too early to say for sure)
  • seasonal flu / influenza: 1.4 - 1.6
  • tuberculosis: 0.26 in the Netherlands; 4.3 in China;
  • leprosy: below 1.0

An aside: even before the vaccine, there were studies that suggested smallpox was dying out on its own. 

So, "we're" all assuming that we need 70% penetration to effect adequate herd immunity when it comes to Chinese flu.


"We" were told that 70% immunity was adequate for the childhood diseases, like measles, chickenpox, and polio. 

And yet, the reproduction numbers for the latter may be 12 - 18, 10 - 12, and 5 -7, respectively.

Wouldn't the herd immunity numbers be a whole lot different for a disease with a reproduction number of 20 vs a reproduction number of 5?

That brings me back to North Dakota: 8% penetration vs 3% for most of the nation. North Dakota ranks first in penetration. South Dakota is second at just below 8%. Hmmm....

Case rate across the US is about 3% -- the number of Chinese flu cases per one hundred subjects runs about 3. 

Spanish flu died out on its own; researchers do not know why. Was herd immunity reached at 33%?

For Spanish flu:

The effective reproduction number (the average number of secondary infectious cases produced by a typical infectious case in a given population) for the 1918 influenza virus was in the range 1.2-3.0 and 2.1-7.5 for community-based and confined settings, respectively.

Hmmm. Interesting. About the same as "seasonal flu" and almost right on the mark for Chinese flu.

Where do you target limited doses of the vaccine? Those most vulnerable and those living in high-density environments.  

Rambling. This and 69 cents will get you a cup of McDonald's coffee via the drive-through.


  1. 82% of deaths in ND - over 70. 15% of deaths were covid related but not covid specific. No breakdown on what constitutes a true covid death. ND used to show what underlying diseases were also present but stopped doing that. CDC lumps covid, seasonal flu and pneumonia all together. Follow the money hospitals/states get.

    If not wearing a mask causes death, many of us old timers should have died 6 months ago. Actually should not have survived childhood. Drank out of hoses, no bike helmets, stayed out after dark, fireworks, etc.

    1. Agree 1000%. The physician only needs to have patient's family give history of Covid-19 exposure and the physician can list Covid-19-related. Yes, that single comment, "Covid-19-related," can generate a nice revenue stream.