# Is the USA approaching herd immunity?

**URL:** <https://boards.straightdope.com/t/is-the-usa-approaching-herd-immunity/932256>\
**Category:** The Quarantine Zone\
**Tags:** covid-quarantine\
**Created:** [February 5, 2021, 11:08am UTC](https://boards.straightdope.com/t/is-the-usa-approaching-herd-immunity/932256 "2021-02-05T11:08:30Z")\
**Posts on this page:** 1\
**Showing post:** 17

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**Author:** ![SayTwo](https://avatars.discourse-cdn.com/v4/letter/s/e56c9b/32.png) [@SayTwo](https://boards.straightdope.com/u/SayTwo)\
**Post date:** [February 5, 2021, 11:51pm UTC](https://boards.straightdope.com/t/is-the-usa-approaching-herd-immunity/932256/17 "2021-02-05T23:51:36Z")

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> [@Stranger\_On\_A\_Train](#):
>
> It is certainly true that there is a skewness in the infection data, and that there are a relatively small minority fraction of infected people who are responsible for the majority of “superspreader” events where dozens or hundreds of people are infected;

Is it, ‘certainly true’? I’m going to hold you to task here, because I’m not aware of any firm evidence of this, despite its widespread belief. Which events do you have in mind, where hundreds of people were infected? (And can you think of any other explanations for what was observed, in those cases?) You talk about surveillance in your post, and despite the US not having the most rigorous data sets from it, there has been plenty of it worldwide. How ubiquitous _is_ this pattern of one person infecting ‘dozens or hundreds’?

My impression is that the contact tracing that’s been done, particularly in places that can do it with genomic sequencing (and thus, at least theoretically, demonstrate something beyond coincidence), points to the vast, vast preponderance of spread coming in other ways.

So, can you provide cites that demonstrate the ‘certainty’ of that purported ‘truth’?

> [@Stranger\_On\_A\_Train](#):
>
> The unmodified basic replication number, R0 (i.e. the mean number of replications per infection) of the original SARS-CoV-2 virus has been estimated at between 3.8 and 8.9, which makes the estimated heard immunity threshold to between 74% and 89% without social and physical modifications to reduce the incidence of transmission. The B.1.1.7 variant has an increase in infectiousness of between 40% and 70% which implies the adjusted herd immunity threshold is between 81% and 94%. Other rapidly spreading variants are believed to have an equal or greater R0 value.

This paragraph is chock full of assumptions and estimates (at least one not expressly described as such), and of course is based on theoretical models (which is not made expressly clear). You are aware of competing models, I would assume? And ones that do better with observed infection data, at that. The simple threshold model you seem to be using here (some might recognize it as similar to something you might see in middle-school algebra) assumes homogenous populations, no? And the real world is far from that?

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