1/ Sweden/Germany had low spread of COVID right now, not because of some magic T-cell immunity, but the result of keeping their R0 below the percolation threshold by diligent contact tracing (Germany) or by luck (Sweden).
Percolation phenomenon of a pandemic is a known idea
Percolation phenomenon of a pandemic is a known idea
2/ Because the spread of COVID19 is driven largely by super-spreaders, R0 is likely not a constant but highly dependent on the density and super-spreading power of superspreader candidates.
3/ consider a map of total population. overlapping blue areas denote people affected by superspreader *candidates* (having tons of high-risk social contacts, but not yet COVID-infected)
too many or too big the big blue dots get (right panel), a single infection can spread to ...
too many or too big the big blue dots get (right panel), a single infection can spread to ...
4/ a big chunk of population, and you have exponential growth of COVID cases.
if blue dots are all small and of low density, local outbreaks die out over time.
if blue dots are all small and of low density, local outbreaks die out over time.
5/ what determines the size of the blue dots? population density & social contacts.
high density cities: Wuhan, NYC, Milan, London, Madrid
large gathering: weekly mega church masses, political rallies, sports events etc.
high density cities: Wuhan, NYC, Milan, London, Madrid
large gathering: weekly mega church masses, political rallies, sports events etc.
6/ Once the majority of the blue dots are connected, infection will sweep through the population. so R0 vs social contact is like the red curve below
there are two R0 for COVID, above threshold maybe 6-8, below threshold may be 1.2
there are two R0 for COVID, above threshold maybe 6-8, below threshold may be 1.2
7/ Sweden has low population density, no mega churches, and thus need low social distancing.
US has cities with high population density, has little contact tracing/isolation, has mega-churches + political rallies. so more social distancing is needed.
US has cities with high population density, has little contact tracing/isolation, has mega-churches + political rallies. so more social distancing is needed.
8/ China did what they did, because they have insane population density.
We don't need China's level of social distancing in the US, but copying Swedish model clearly has not worked (e.g. in Texas), for a good reason!
We don't need China's level of social distancing in the US, but copying Swedish model clearly has not worked (e.g. in Texas), for a good reason!
9/ That's all I can write in the middle of a trading day. H/T to @profvrr and @c_drosten. @profvrr and @bioprofba
may cover this topic again in the next TwiV episode.
If not, I might write something next week to explain this idea a bit more.
may cover this topic again in the next TwiV episode.
If not, I might write something next week to explain this idea a bit more.
10/ The bottom line is that we need testing and good epidemiology data to figure out the appropriate level of social distancing for different cities.
We are largely flying blind and we get the worst of both worlds:
too many infections/deaths
and unnecessary economic suffering
We are largely flying blind and we get the worst of both worlds:
too many infections/deaths
and unnecessary economic suffering
I misspelled Brianne's handle @BioProfBarker here.
unless people in power want the worst of both worlds to push for
unnecessary Fed money printing
and Trillionaire enrichment
unnecessary Fed money printing
and Trillionaire enrichment
