COVID19 update, June 30, 2020: droplet and aerosol transmission; herd immunity requires as little as 20%?

Been a very busy day at work, but let me just share with you two things:

(a) a long essay that Jeff Duntemann drew my attention to:

Aerosols, Droplets, and Airborne Spread: Everything you could possibly want to know by Justin Morgenstern MD, an emergency physician located in the greater Toronto area.

The essay is long but very much worth your while.

(b) Coronavirus: could it be burning out after 20% of a population is infected? We pointed earlier to a preprint that showed that, if susceptibility to the infection isn’t assumed to be all or nothing, that this leads to a second-order mathematical model that predicts much lower herd immunity thresholds than the common first-order model. See also (h/t: masgramondou): https://judithcurry.com/2020/05/10/why-herd-immunity-to-covid-19-is-reached-much-earlier-than-thought/ 

But it is unlikely that lockdowns alone can explain the fact that infections have fallen in many regions after 20% of a population has been infected – something that, after all, happened in Stockholm and on cruise ships. 

That said, the fact that more than 20% of people have been infected in other places means that the T-cell hypothesis is unlikely to be the sole explanation either. Indeed, if a 20% threshold does exist, it applies to only some communities, depending on interactions between many genetic, immunological, behavioural and environmental factors, as well as the prevalence of pre-existing diseases. 

Understanding these complex interactions is going to be necessary if one is to meaningfully estimate when SARS-CoV-2 will burn itself out. Ascribing any apparent public health successes or failures to a single factor is appealing – but it is unlikely to provide sufficient insight into how COVID-19, or whatever comes next, can be defeated.

3 thoughts on “COVID19 update, June 30, 2020: droplet and aerosol transmission; herd immunity requires as little as 20%?

  1. Lots of food for thought!
    (droplet and aerosol transmission. This was dense enough that I had to read it twice and no time yet to read about the herd immunity figures)

  2. https://jbhandleyblog.com/home/2020/6/28/secondwave

    LOCKDOWN LUNACY 2.0: Second wave? Not even close.

    The headlines are filled with dire warnings of a “second wave” and trigger-happy Governors are rolling back regulations to try to stem the tide of new cases. But, is any of it actually true and should we all be worried? No, it’s not a second wave. The COVID-19 virus is on its final legs, and while I have filled this post with graphs to prove everything I just said, this is really the only graph you need to see, it’s the CDC’s data, over time, of deaths from COVID-19 here in the U.S., and the trend line is unmistakable:

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