One of the buzz phrases in the obsessive discussion of the
virus is “herd immunity.” Herd immunity, as I understand it, is the protection
one gets from an infection when one is part of a population so large a portion
of which is immune and not transmitting the infection that the probability of
contracting the infection becomes, if not zero, acceptably low. I don’t know
from nothing about epidemiology so I will simply accept the commonly repeated
statement that in order to achieve some measure of herd immunity a population
must be at least 60% immune and not transmitting. At the moment there are
roughly 4 million confirmed cases of COVID-19 in the United States but it is
widely estimated that as many as 10 times that number have actually contracted
the virus and either have it in active form now or have recovered from it and
are immune. So let us assume that 40 million Americans have or have had the
virus. 60% of the American population is roughly 200 million people so by these
calculations we are 1/5 of the way to herd immunity. At the moment, there are
almost 150,000 confirmed deaths from the virus. Many commentators assert with
confidence that the real number is rather larger but assume that 150,000 is
correct. In the absence of a vaccine, that means that by the time the United
States population achieved the lowest level of herd immunity, a total of 750,000 people would have died from contracting the virus.
That number of deaths in addition to all the
other deaths routinely suffered would constitute an increase in the death rate
for a year of roughly 33%.
12 comments:
As I understand it, herd immunity is based on the assumption that, if you are infected and survive, your immune system has produced antibodies that protect you from being re-infected by the same virus. That may not be the case with Covid19. Apparently, the jury is still out on that one.
Immunity may be lost in months, per the first study of its kind.
Yes, it seems that the normal concept of immunity does not really apply to this virus. Very short-lived, and it seems there is a lot of anecdotal evidence of re-infection weeks or even days after recovery from the first experience.
And your numbers are off - it is ~150k counted deaths at the moment, not 250k.
I find, as of this moment, 148k deaths with 1,150 having been added from the previous day.
"Data comes from sources like Wikipedia, government health ministries, The New York Times, and other authoritative sources, which may be added over time with attribution. Cases are constantly updated from resources around the world. Daily situation reports are also available on the World Health Organization site"
However, the actual number may be closer to 250k given the massaging of the numbers lower.
It is sad cause there are more dead americans than during the korean war and the vietnam war together.
Anonymous is correct, and I have revised the post accordingly. My mistake. Thank you.
In addition to what commenters have already pointed out (post-infection immunity is not a sure bet) I'm pretty sure the standard herd immunity percent is north of 70%.
As I understand, immunity depends on more than just antibodies. There are also specialised immune system cells called T-cells and B-cells that play a major role = see for an introduction
https://www.ncbi.nlm.nih.gov/books/NBK459471/
AFAICT (not being medically trained in any way) the fading of the antibody response after a few months is not surprising and does not necessarily imply renewed vulnerability to the virus. In fact, again AFAICT, there seems some evidence *for* a long term immunity against Covid19 - see this paper in Nature:
https://www.nature.com/articles/s41586-020-2550-z
Two factors that may complicate the arithmetic are:
On the good side, discovering effective treatments might lower the death rate (e.g. dexamethsone)
On the other side, there are now many reports of long-term problems caused by the virus - fatigue, shortness of breath and unfortunately sometimes worse:
https://covid.joinzoe.com/post/covid-long-term
Off topic, but I seem to recollect you liked the earlier part of Hans Sluga's intellectual odyssey. This part brings him to Berkeley, to his encounter with the question why so many German philosphers of diverse commitments took to Nazism, to his warning Foucault about the emerging AIDS epidemic, and more:
http://www.truthandpower.com/blog/blog/berkeley-years/
But the crucial point about herd immunity is that it is usually achieved through mass vaccination rather than by letting a virus go through a population - at least that's the safest way.
I thought the consensus was that the death rate for real as opposed to recognised cases worldwide was something like 1%. (The *recognised* death rate for *recognised* cases in the US is nears 3.5%.) So for the USA to achieve herd immunity at 60% of the population, about two million people would have to die. That is two million would have to die DIRECTLY of Covid: the knock-on death toll would be a fair bit higher.
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