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<p>A contagion dies out when the replication factor R drops below 1,
i.e.:<br>
</p>
<p>R = Ro U < 1<br>
</p>
<p>Ro is the "normal" number of people a person can infect.<br>
U is the proportion of the population that can still be infected</p>
<p>The UK Covid figure for Ro was around 3 (before social
distancing)</p>
<p>So in a "do nothing" scenario</p>
<p>R <= 1, when U= 1/Ro= 1/3</p>
<p>i.e. when (1-U)=67% of the population has been infected.</p>
<p>If interventions (like distancing, testing, quarantine) can make
Ro < 1, the contagion will die out without infecting the whole
population.<br>
(as seen in New Zealand).</p>
<div class="moz-cite-prefix">On 06/05/2020 17:41, Peter Bernard
Ladkin wrote:<br>
</div>
<blockquote type="cite"
cite="mid:e08b3508-ce5b-96ca-fe0c-3f0b0a270ec9@causalis.com">
<pre class="moz-quote-pre" wrap="">
On 2020-05-06 18:14 , RICQUE Bertrand (SAFRAN ELECTRONICS & DEFENSE) wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">May be that, as in safety for accidents, it is a question of time?
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">Very unlikely. Even the Plague, which was almost invariably fatal, only killed off 1/3 of the
population of Europe (and brought an end to feudalism). Given living conditions at the time, we can
presume most people in cities were exposed to Yersinia. But only a third got the disease.
PBL
Prof. Peter Bernard Ladkin, Bielefeld, Germany
Styelfy Bleibgsnd
Tel+msg +49 (0)521 880 7319 <a class="moz-txt-link-abbreviated" href="http://www.rvs-bi.de">www.rvs-bi.de</a>
</pre>
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<pre class="moz-signature" cols="72">--
Peter Bishop
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