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NNadir

(33,368 posts)
Fri Aug 14, 2020, 11:17 AM Aug 2020

A mathematical model reveals the influence of population heterogeneity on herd immunity to SARS-CoV2

The paper to which I'll refer is this one: A mathematical model reveals the influence of population heterogeneity on herd immunity to SARS-CoV-2 (Tom Britton1,*, View ORCID ProfileFrank Ball2, View ORCID ProfilePieter Trapman1, Science 14 Aug 2020: Vol. 369, Issue 6505, pp. 846-849)

The scientific publishing community has made all SARS-Cov-2 papers open sourced. There is no need for me to excerpt all that much of it, but it does note that something that all of here know, even if the ignorant white supremacist in the White House is as clueless on this subject as he is on all others: In diversity is strength.

The paper, however, does not actually refer to ethnic diversity, but rather to diversity in age and activity levels, as well as the diversity in restrictions utilized. This, of course is good news.

A few brief excerpts:

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread globally despite the many different preventive measures that have been put in place to reduce transmission. Some countries aimed for suppression by extreme quarantine measures (lockdown) and others aimed for mitigation by slowing the spread using certain preventive measures in combination with protection of the vulnerable (1). An important question for both policies has been when to lift some or all of the restrictions. A closely related question is if and when herd immunity can be achieved. Herd immunity is defined as a level of population immunity at which disease spreading will decline and stop even after all preventive measures have been relaxed. If all preventive measures are relaxed when the immunity level from infection is below the herd immunity level, then a second wave of infection may start once restrictions are lifted.

By 1 May 2020, some regions and countries reached high estimates for the population immunity level; for example, 26% of the population was infected (with a large confidence interval) in the metropolitan Stockholm region, as shown by a mathematical model (2). At the same time, population studies in Spain showed that in the second half of May 2020, >10% of the population of Madrid had antibodies for coronavirus disease 2019 (COVID-19) (3). It is debatable whether (classical) herd immunity for COVID-19, which is believed to lie between 50 and 75%, can be achieved without unacceptably high case fatality rates (4–6).


There is then a discussion on the likely impact of vaccination on herd immunity, depending on the efficacy of the vaccine.

A figure from the paper:



The caption:

Fig. 1 Overall fraction infected over time.
Shown is a plot of the overall fraction infected over time for the age and activity structured community with R0 = 2.5 for four different preventive levels inserted 15 March (day 30) and lifted 30 June (day 135). The blue, red, yellow, and purple curves correspond to no, light, moderate, and severe preventive measures, respectively.


An interesting read, I think.

Have a nice weekend.
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