Why Herd Immunity to COVID-19 is Reached Much Earlier Than Thought – Update

By Nic Lewis – Re-Blogged From WUWT

I showed in my May 10th article Why herd immunity to COVID-19 is reached much earlier than thought that inhomogeneity within a population in the susceptibility and in the social-connectivity related infectivity of individuals would reduce, in my view probably very substantially, the herd immunity threshold (HIT), beyond which an epidemic goes into retreat. I opined, based on my modelling, that the HIT probably lay somewhere between 7% and 24%, and that evidence from Stockholm County suggested it was around 17% there, and had been reached. Mounting evidence supports my reasoning.[1]

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Why Herd Immunity to COVID-19 is Reached Much Earlier Than Thought

By Nic Lewis – Re-Blogged From Climate, Etc

Introduction

A study published in March by the COVID-19 Response Team from Imperial College (Ferguson20[1]) appears to have been largely responsible for driving government actions in the UK and, to a fair extent, in the US and some other countries. Until that report came out, the strategy of the UK government, at least, seems to have been to rely on the build up of ‘herd immunity’ to slow the growth of the epidemic and eventually cause it to peter out.

The ‘herd immunity threshold’ (HIT) can be estimated from the basic reproduction rate of the epidemic, R0 – a measure of how many people, on average, each infected individual infects. Standard simple compartmental models of epidemic growth imply that the HIT equals {1 – 1/R0}. Once the HIT is passed, the rate of new infections starts to decline, which should ensure that health systems will not thereafter be overwhelmed and makes it more practicable to take steps to eliminate the disease.

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The Pandemic: Cardinal Numbers No One Talks About

By Vinay Kolhatkar – Re-Blogged From Savvy Street

It’s plausible that somewhere between 100 million and 500 million people on earth have had, or are having, the coronavirus infection.

That is a staggering statement when, as at April 19, 2020, the confirmed cases numbered 2.35 million. And we are projecting that somewhere between 40 to 200 times that, is the real number, which is between 1.3% and 6.5% of the world population.

What’s the reasoning behind how we may have gotten there? And what’s the evidence?

Let’s go through the reasoning first.  Continue reading