If I might, one or two points.
Some people think that "an N95 mask is only 95% efficient, so 5% of the
viruses will get through, and it only takes ones to infect you".
That is both true and not true at the same time. True in that an
infection can begin with one virus, but not true in the sense that if
you breathe in one virus you will get a disease - you almost certainly
won't.
We don't know exactly how many it takes on average, but most individual
viruses you inhale will just not reach the stage of starting to
multiply. They get killed or trapped or exhaled or digested or just fail
to reach the right spot (typically an ACE receptor on a lung type 2
pneumocyte).
Think on it this way, an N95 mask makes it at least twenty times less
likely that an average interaction with the virus will infect you.
Another misconception, and it is a biggie, if not the biggie - we do not
know the crude case fatality ratio with any confidence. The cfr is the
number of deaths divided by the number of cases.
We can make some assumptions about the number of deaths - many cases
have not yet had enough time to die or recover, so the crude numbers can
be misleading, but we can say roughly speaking that five weeks ago x
people who were infected will die/have died, depending on POV.
However we don't really have much of a clue about the actual number of
cases, either now or five weeks ago. We know about notified cases, but
there are at least some unnotified cases, we just don't know how many.
If we run the raw numbers we get about 3.7% worldwide - but from hints
in Vo and the Diamond Princess cruise ship, it seems that an upper limit
of something less than 1% is what is really happening, implying that
there are at least four times as many actual cases as known cases.
Data from Korea, and recent data from Germany suggests that a rate of
about 0.5% is perhaps more appropriate, suggesting that worldwide nine
out of ten cases are unreported, probably because their symptoms are slight.
It is just possible that it may turn out to be less even than that.
"The overall case fatality rate as of 16 July 2009 (10 weeks after the
first international alert) with pandemic H1N1 influenza varied from 0.1%
to 5.1% depending on the country. The WHO reported in 2019 that swine
flu ended up with a fatality rate of 0.02%. Evaluating CFR during a
pandemic is a hazardous exercise, and high-end estimates end be treated
with caution as the H1N1 pandemic highlights that original estimates
were out by a factor greater than 10." [1]
But don't rely on it.
This is both very good news and a lot of bad. Good because potentially
many less people will die than we thought (if good medical care is
available), bad because it means that the present spread is much larger
than thought, it will now or soon be very difficult to stop, and
hospitals will be stretched sooner rather than later, and stretched more
than expected. If, as in Italy, care becomes unavailable, then many
people will die unnecessarily.
Stay home, stay safe.
Peter Fairbrother
[1] https://www.cebm.net/global-covid-19-case-fatality-rates/