First, I want to pass along these items from Sam LeFevre, a reader of this blog and, if I’m not mistaken, the director of the Bureau of Epidemiology in the Utah Department of Health. I share them with his kind permission, and with the understanding that they represent his opinions and do not speak for the State of Utah, because I think that what they have to say is urgently important:
There is a formula that is used by epidemiologists to determine what level of herd immunity is needed to control the virus. The formula is 1 – (1/R0). R0 (R naught) is the wild reproductive factor of the virus (where “reproductive” refers to the ability to generate cases of infection and disease, not viral progeny). For COVID the wild R0 is thought to be between 2.4 and 3.1, with a pooled analysis saying it was about 2.7. This suggests that we need about 63% of the population to either have effective natural immunity (I’ve recently described what “effective” means elsewhere) or acquired (vaccine induced) immunity. That level of herd immunity needs to be uniform across the whole population.
If the level of immunity is not uniform (say 80% in Salt Lake City, and 40% in Provo), wherever there are pockets where the virus is able to continue to propagate, the likelihood of the emergence of a variant that can escape immunity increases. RNA viruses mutate fast. We already have the emergence of foreign variants that can partially escape immunity. The latest is the double mutation variant from India (B.1.617) and the even more troublesome French variant (“le variant Breton”).
My fear is that those who resist vaccine put the whole state population at risk of going through this whole ordeal again. And I don’t think I can survive another year like the last (I’m tired of the hate mail).
Anyway, some might find this interesting: Five reasons why COVID herd immunity is probably impossible, Nature, March 18, 2021..
Heading off the accusations: I am sharing this not to incite fear (although I’ve admitted I have some). I am hoping to just provide some educational information and perhaps some incentive.
Disclaimer: These thoughts are my personal opinions. Hopefully somewhat informed opinions that others might find profitable. I do not represent or speak for any state government agency or policy-making body.
More about R0 and Rt. Rt is the current reproductive number. It is most useful in forecasting models, but has an additional interpretation. If Rt is greater than 1.0 the epidemic is growing and out of control. If Rt is less than 1.0 the epidemic is declining and in control. The lower the Rt, the better the control.
The whole idea behind the non-pharmaceutical interventions (or NPI = mask wearing, social distancing, gathering restrictions, etc.) was to “flatten the curve” OR reduce the Rt, until a pharmaceutical intervention (anti-viral drugs, vaccine, monoclonal antibodies) could be developed.
If one is interested, one can find a reasonable estimate of the current Rt for Utah here (click on the map): National and Subnational estimates for the United States of America.
Check this again in about 14 and 28 days to see what the ending of the mask mandate did.
I haven’t been doing as well at sharing these valuable materials from Jeff Lindsay as I should have been: