By Nic Lewis
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.
I then showed in a July 27th update article[1] that mounting evidence supported my reasoning.
It is pleasing to report that the evidence for heterogeneity of susceptibility across the population, arising from variability in both social connectivity and biological susceptibility, has continued to increase. Not least, there have been a number of further papers reporting pre-existing cross-reactive T-cells in a substantial proportion of people, which as I discussed in my July 27th article is likely be a key reason for heterogeneity in biological susceptibility. Mainstream journals are now starting to acknowledge that these factors are significant, with the implication that the herd immunity threshold (HIT) can be expected to be substantially lower than that often quoted by scientists close to governments. Unfortunately, in the UK at least, there is little sign as yet that those scientific advisors are prepared to recognise these facts.[2] [3]
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