Wondered about such things and just looked
into the subject.

In simple terms, here in the US, we only
have a little data. E.g., apparently a
big fraction of the data we have closely
relevant to these questions is in
a US CDC report

"Severe Outcomes Among Patients with
Coronavirus Disease 2019 (COVID-19) —
United States, February 12–March 16, 2020"

that is, to essentially the present and
only 4 days more than a month.

Can see the report with a lot of words
with actual numerical values at

https://www.cdc.gov/mmwr/volumes/69/wr/mm6912e2.htm

and, then, can see their graph of
hospitalizations, ICU admissions, and
deaths by age in Figure 2 at

https://www.cdc.gov/mmwr/volumes/69/wr/mm6912e2.htm#F1_down

For how many people are infected, tough
to know before we test a good simple
random sample with a good test. From some
of what Dr. Brix said recently, our
test(s) "amplifies* the genetic code and
sequences that.

If I understand correctly, the
amplification is via the PCR where From
Google,

"Polymerase chain reaction (PCR) is a
method widely used in molecular biology to
rapidly make millions to billions of
copies of a specific DNA sample allowing
scientists to take a very small sample of
DNA and amplify it to a large enough
amount to study in detail. PCR was
invented in 1983 by Kary Mullis."

So, the test is not trivial, is some
microbiology that, say, before 1983 would
have seems impossible.

Next Dr. Brix has indicated that the US
is very careful about the rates of false
positives and false negatives of the tests
they use.

Still, for now, apparently we don't know
how many people in the US are (or have
been) infected.

But from the CDC data above, we have some
okay data (numbers are still small for
accurate statistical estimates) by age of
the fraction of hospital admissions with
the virus that got into an ICU and then
the fraction that died.

Considering the US population over 65, how
big is that?

Uh, from Google search

"US population over 65"

get

"49.2 million

In the United States, the population age
65 and over numbered 49.2 million in 2016
(the most recent year for which data are
available). They represented 15.2% of the
population, about one in every seven
Americans."

So, the US has to try hard to stop the
spread of the virus or, ballpark, the US
is looking at about 50 million citizens
(a) nearly all of whom would get the virus
and (b) a significant fraction of whom
would die if they are like the people in
the data who got the virus and were
admitted to a hospital.

Net, bottom line, if extrapolate from that
CDC data, then the US has to be careful or
a lot of people over 65 could die:

In more detail, from the reference with
the words,

"This first preliminary description of
outcomes among patients with COVID-19 in
the United States indicates that fatality
was highest in persons aged =85, ranging
from 10% to 27%, followed by 3% to 11%
among persons aged 65–84 years, 1% to 3%
among persons aged 55-64 years, <1% among
persons aged 20–54 years, and no
fatalities among persons aged =19 years."

Or, it could be > 3% dead of people over
65.

So, 3% dead of 50 million would be 1.5
million. If want to use the 10% number in
the CDC text, then that would be 5 million
dead.

So, hurry up step #1 is to slow the spread
of the virus by a lot of social distancing
and hand washing.

Hurry up step #2 is look for cures by (a)
trying old drugs to see if any are
effective against the virus, (b) get some
antibodies from some people already cured
from the virus and see if those antibodies
can be the basis of a cure, (c) starting
with the microbiology, e.g., the molecular
geometry, of part of the virus, try to
construct an antibody.

Step #3 -- ASAP get a safe and effective
vaccine and give nearly everyone a shot.

In case #1 to #3 happen too slowly, do #4,
get hospitals ready for lots more
patients.

Unlike some other diseases, some good news
about this virus is that everyone who gets
the virus can transmit it for only a few
weeks.

So, in simple terms, if the world would be
100% effective at social distancing for a
few weeks, then the world would be free of
the virus! And if the world is close to
100% effective, then the world will still
be free of the virus soon!