What We Know (And Don’t) About
COVID 19
By Ken Karch, MPH
Updated May 9, 2020 Ver.5.0
(Updated material (since 4/25/2020) highlighted)
1.
Members of the
general public may be infected by droplet spread from other individuals;
there is little evidence that infection can come from animals such as pets,
except through intermediate contact with other persons who are infected (an
announcement a couple of
weeks ago of an apparent COVID-19 case in a tiger at a Bronx (NY) zoo and
two house cats in New York are being investigated). There is evidence that the
COVID-19 virus is a zoonosis (animal to human spread), and that the initial
breakout occurred from a bat population to humans thru a wild meat market or
virology lab in China. From there it
apparently found its way to other countries by person-to-person contact.
2.
Droplets are
those which we are told have an effective distance of no more than 6 feet;
therefore, individuals are asked to maintain a social distance of 6 feet
3.
We do not know
whether fine, dry particles containing the virus can survive, and become
infective beyond a 6 foot distance. My MPH training indicated that the
effective distance of sneeze particles is 15 feet. Others have suggested that it may be up to 27 feet, or that the
virus may be pervasive and
infective throughout the general atmosphere near a carrier…this is usually
called aerosolized. There is some
evidence that smaller virus particles can be transmitted through
normal talking or breathing. Smaller particles (less than 1 micron) are
most effective in entering the lungs.
The virus particles attach to lung membranes and create a reaction which
damages the ability of the lungs to function properly, causing difficulty in
breathing, inability to transfer
oxygen, damage to other organs, and sometimes death. The definitions of direct transmission,
indirect transmission, droplet spread, and aerosolization are understood and
used differently by different people, particularly the media. Recent studies have indicated that the
COVID-19 virus is particularly susceptible to sunlight, moisture, and temperature. Droplet spread
diseases include the common cold, flu, meningococcal disease, and rubella,
while aerosol diseases include chickenpox, measles, and tuberculosis.
4.
We are told that
face masks are effective, somewhat effective, or not effective by
different experts, that such protection varies with the materials from which
the mask is made, and the fit, and that the protection may be different between
outgoing vs. incoming infective agents.
General guidance currently suggests that most face masks may be somewhat
effective in preventing or reducing infectious agents from passing from the
wearer to others, rather than from others to the wearer. Therefore, it requires a social commitment of
the potential wearer to protect others.
It is not clear whether all, many, some, or no potential wearers
understand this, or accept such a social contract. We have been warned of the risk that mask
wearers may be lulled into a false sense of security by wearing a mask,
and ignore other social distance recommendations. Beyond that, pop-up makers of cloth masks
tell you that cloth is the only reliable media for masks, and they try to sell
them as a protection for the wearer. Standards exist to measure the effectivenss
of face masks, with cloth masks about 50% effective in reducing virus
particles, provided they are properly worn and maintained.
5.
Although
COVID-19 appears to infect all ages, we know that elderly persons, and
others with compromised immune systems, and other underlying health conditions (which is poorly
defined and quite broad) have a greater risk of death, once they are
infected. Typical case fatality rates (CFR)
are at or about 15% in those populations, and less than 5% in other
populations. The CFR from March 6 to March 10 in Washington State from the
Kirkland care facility was about 15%; since then it dropped to around 4% before
rising slowly to 5 to 6%. Deaths are
a lagging indicator to identified cases, so persons infected during the
early March timeframe were not dying until mid- to late March. The same pattern
emerged in Pierce County, where the current CFR is between 3 and 4%, and had
been below 2% since early March. Pierce
County did not experience an initial “bump,” and may have escaped the rapidly
rising case and death numbers experienced from Kirkland (which dominated the
King County, State of Washington, and even the US reported data for the first
10 days of March), since social distancing and other measures were widely
recommended before those who would have been infected in early March would
already have exhibited corresponding death rates in late March. Beyond this,
the reporting of morbidity and case fatality rates is likely skewed due to
decisions to address risks to health care workers and those with symptoms or
immune system issues (the most likely to have the disease) first. As a result, future morbidity and mortality rates
may in fact drop further.
6.
COVID-19
reported death rates fall disproportionately among older persons and persons
with other diseases or immune system disorders.
The “outbreaks” resulting in COVID-19 deaths in this population are
considered “premature deaths;” and reduce the number of deaths of some
fraction of the same persons from other causes during the same or later time
frames. To put it bluntly,
if I die today of something, I can’t die tomorrow of something else.
7.
We are told that
the usual “incubation period” of COVID-19 probably does not exceed 14
days (though some say it is longer), but that a period of infectivity may begin
before symptoms are apparent to the infected individual or others, with
infectivity being greatest in the middle of the period (presumably something
akin to a “bell-shaped curve”); and with greatest infectivity in, say, the 6th
to 10th day.
8.
We do not know
whether persons who have contracted the virus (and tested positive) and
recovered, have acquired immunity for future attacks of the same, or
similar, viruses, or whether such immunity may be short-term or longer term. Until we acquire case and death data from a
greater proportion of the general population, we will be only guessing about herd
immunity. Beyond that,
a debate exists between those who believe the proper approach is to quarantine
those who have been diagnosed with COVID19 or are especially susceptible to it (a
fraction of the population in the few percentages of the total), and therefore
allow herd immunity to develop among the rest, a large fraction of whom will
exhibit little or no symptoms in the process (the examples of tour boat and
military ship outbreaks are instructive here).
The arguers for this position say the current efforts to quarantine
virtually the entire population, with ensuing economic, social, religious, and
political impacts, will virtually assure that a second and third harmonic of
cases and deaths will occur, once restrictions are lifted.
9.
The role of
government in requiring vaccination may prove crucial in the future, once an
effective, safe, vaccination protocol is found. A case in point is the
difference between the mandatory vaccination laws governing childhood
diseases (with some religious and other exceptions, recently changed in
Washington State law), versus the voluntary flu vaccination recommendations.
10. We do not know whether, or the extent to which, the
virus may mutate to other more (or less) dangerous forms. There is some
evidence that such mutations are not uncommon.
11. We know that COVID19 virus community episodes seem
to behave as other viruses and communicable diseases do, namely a logarithmic
growth phase, a leveling off period, and a decline. The slopes of the lines give the best
evidence of the place a community is in on the curve; the area under the curve
represents the total extent of the pandemic (classical differential and
integral calculus is in play here). This
is why we are urged to take necessary steps to “flatten the curve”
(thereby spreading it out in time to give more time to deal with shortages and
take other preventive and treatment steps).
12. The primary means of prevention, in the absence of
vaccination, is social distancing for communicable diseases. Daniel Defoe, in The Journal of the Plague
Year, in 1722, described the effectiveness of social distancing by recounting
the different results around London in 1665 between those who escaped the city
to country places, versus those who were forced (literally) to remain in
crowded dwellings with their families, often resulting in the death of the
entire family.
13. The future of the pandemic is largely unknown. It is complicated by the fact that we have
tested less than 2% of the population; those tested are skewed toward health
care workers and high susceptibility persons; of those tested about 4 to 15%
test positive; of those testing positive, death rates range from 2 to 20%; we
don’t know how many asymptomatics are out there; we don’t know whether, when,
and the degree to which asymptomatics are shedding virus; nor the effectiveness
of preventive measures such as social distancing and masks; treatment
modalities; or the expectation of vaccines. It is further complicated by the
fact that virtually all data comes in from 50 or more different (e.g., state
and local) agencies, each of which has its own set of priorities, capabilities,
and epidemic management plans (did someone say something about herding cats?). We don’t know the recovery rate of
symptomatics or asymptomatics. We don’t know whether asymptomatics secure
immunity from future attacks.
“Flattening the curve” of deaths will follow “flattening the curve” of positive
cases by some number of days, and once the curves are flat, new cases and
deaths will continue to follow while the numbers return to near zero, and may
very well equal or exceed cases and deaths up to the “plateau” or “apex.” Furthermore, relaxation of the prevention
tools may result in a second and third outbreak, as occurred in the 1918 flu
epidemic and others.
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