[ExI] What about the Aussies

[Rafal Smigrodzki]

On Thu, Apr 8, 2021 at 6:07 AM Stathis Papaioannou <stathisp at gmail.com>
wrote:

>
> What about Australia and New Zealand?
>
>>
>
### There are at least three factors involved here: Geographic isolation,
timing of the austral summer and stochasticity of viral spread at low
numbers of infected persons. While the Wuhan virus spread rapidly during
boreal winter of the Northern hemisphere, its initial appearance coincided
with the austral summer and its spread was thus slowed down in the Southern
hemisphere. Since Australia and NZ are geographically isolated there were
few seed cases and their R0 was limited by the summer weather. With a low
number of cases an epidemic is stochastic - it can spread or peter out
randomly. Add strict lockdown and the likelihood of the epidemic petering
out is higher, even in a genetically susceptible population of European
ancestry.

It is however instructive to compare Australia and NZ to Chile and
Argentina - in these countries the virus eventually spread widely, despite
draconian lockdowns - but it was out of phase with most Northern hemisphere
countries (I am giving links to my Google Drive here, graphs are copies
from ourworldindata):

https://drive.google.com/file/d/1tef_-cP_-uEWBhp53xx4oOXllJ4NeUVG/view?usp=sharing

Argentina and Chile did not benefit from geographic isolation as much as
A&NZ, so eventually the virus just exploded there, once the austral winter
came. Interestingly, both Australia and NZ had a slight bump in cases
during austral winter but both petered out - the number of cases was a
couple of orders of magnitude below Chile and Argentina (remember that the
population of continental South America is 400 million people with some
permeability of borders, so the absolute numbers of cases were orders of
magnitude higher, more so than you might deduce simply by looking at the
graph above which is normalized to deaths per capita).

It's instructive to look at the phases of pandemic in various countries.
Phases of spread will be influenced by timing of seed cases in relation to
local climate. Some countries, for example, UK and US, were seeded with
large numbers of cases early on during winter, resulting in a rapid spread,
then reduction of cases in the summer, then again massive outbreaks in the
following winter, until approaching herd immunity (biphasic spread). Others
like Poland and Chechia did not have many seed cases early on and nothing
happened there in winter-spring 2020 but eventually they suffered
staggering outbreaks in fall 2020-winter 2021 (monophasic spread):

https://drive.google.com/file/d/1Xcijh-0fTDOtYs0YdyDLg9oM4aGZy0IP/view?usp=sharing

It's also instructive to look at the cumulative deaths in these countries -
regardless of monophasic or biphasic spread, the cumulative deaths trend to
a similar level eventually:

https://drive.google.com/file/d/1qOuUm_7nIT3lsJENdK9mVGKgeWxBdluT/view?usp=sharing

It's also useful to look at countries that differ in their public health
policies and their eventual outcomes - if you compare Sweden and the
Netherlands with their laissez-faire approaches to the pandemic with the
US, Germany, Poland and the UK with their insane Gestapo policies, there is
no difference:

https://drive.google.com/file/d/15K2R9zUcvq9TIEPfEovXCN1L_YrMK2t2/view?usp=sharing

Now, there are outliers and mysteries. Look at this map:

https://drive.google.com/file/d/18M_neJttyEXawVSMiMaak-GsgIeqwu-g/view?usp=sharing

Why did Finland and Norway have so few cases? Dunno. Why is all of Africa
seemingly doing so much better, except South Africa? Blacks in the US
suffer from Covid greatly, so it shouldn't be genetics that explains low
numbers for Africa - but then, Blacks in the US are not that black, with
25% European ancestry on average IIRC. Maybe it's because blacks in Africa
are thinner than their US cousins? We know obesity is a risk factor for
severe Covid infection, so maybe that's the explanation. Or maybe African
nations, being poor, just don't keep track of Covid deaths. But what about
the Arab world? Sky-high obesity rates but hardly any cases? Does something
about being Arab protect you from the virus but being Persian doesn't?
Maybe, Persians are closer genetically to Europeans, so maybe that's why
Arabs get fewer infections. But why do Jews in Israel get more infections
than Arabs in most Middle Eastern countries? Is it the European admixture
in the Ashkenazim? Who knows.

There is a lot of uncertainty but a few points can be made with reasonable
confidence:

1) Infection that affects few people is stochastic. The number of cases
will fluctuate randomly, occasionally reaching zero - which means the
epidemic ends. However, once a pandemic reaches a sufficient level of cases
it is no longer stochastic, it becomes exponential and it will spread until
herd immunity is reached, whether by surviving the infection, by culling of
susceptible individuals and their genomes, or by vaccination.
2) Geographic isolation and effective size of the population play a role in
the timing of initial cases and the likelihood of stochastic extinction of
disease.
3) The course of the pandemic is often influenced by climate, especially
with diseases spread by aerosols.
4) The eventual outcome in terms of cumulative deaths per capita is
determined primarily by the susceptibility of the population. The genetic
part of susceptibility exceeds other modifying factors by orders of
magnitude in the Wuhan virus, with European and Amerind populations having
highest susceptibility and East Asians having the lowest susceptibility,
and with substantial uncertainty (so far) regarding other clades.

Rafal
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