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There seems to be a common fundamental misunderstanding of the concept of herd immunity, which leads to unhelpful cross talk. Herd immunity is not more (or less) a harmful concept than heredity or gravity. It is neither a strategy nor a policy.
1/ https://twitter.com/andymoz78/status/1312480693692162048
1/ https://twitter.com/andymoz78/status/1312480693692162048
Herd immunity (HI) is the mathematical relation between the proportion of the population being immunised (through infection or vaccination) and the transmission of a pathogen. In its simplest form, it reads HI=1-1/R, with R being the reproductive number of the pathogen.
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Any fraction of the population being immunised reduces transmission of a pathogen, proportionally so. The 'herd Immunity threshold' is a mathematical inflection point when a sufficient proportion of the population is immunised, through infection or vaccination, so that R≤1.
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To many, including scientists, herd immunity seems to be 'how we eliminated measles through vaccination'. This is not a meaningful definition and measles is not even a particularly good example for herd immunity.
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Measles is one of the very few pathogens providing near life-long immunity but is also exceptionally contagious (very high R). Measles was primarily eliminated through global mass-vaccination rather than herd immunity.
Source: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(17)30307-9/fulltext
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Source: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(17)30307-9/fulltext
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Herd immunity helps keeping in check more than >200 respiratory viruses in circulation and contributes to their seasonality. It is also the main force driving pandemic influenza strains (e.g. 1918, 1957, 1968) into endemic seasonal flu.
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Herd immunity is at the heart of any meaningful mitigation strategy against #COVID19 irrespective of the proportion of the population who will get immunised through vaccination or infection. Vaccines are generally not suitable for everyone (e.g. immunocompromised)
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To allow future constructive discussions, it would be helpful to stick to the science and avoid politicising 'technical terms'. I appreciate this battle is probably lost for 'herd immunity', which arguably sounds awful. Thus, I suggest we use 'community immunity' from now on.
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