The surviving population is [(1-P)+P(1-pd)]. To have herd immunity, we need the infection to slow down among non-infected people, so {(1-P) / [(1-P)+P(1-pd)]} * R0 < 1 Thus: P > (R0 - 1)/(R0 - pd) When R0=2, pd=3%, we have P>50.76% When R0=2, pd=4%, we have P>51.02% When R0=2.5, pd=3%, we have P>60.73% When R0=2.5, pd=4%, we have P>60.98% Hence, the conclusion that 60% infection is needed for the herd immunity can be made by R0=2.5, pd=3% to 4%.
CNN 新闻： Here's one estimate by Dr. James Lawler at the University of Nebraska Medical Center: On March 5, he predicted that over the next two months, 4.8 million patients will be hospitalized in the US because of the coronavirus -- including 1.9 million stays in the intensive care unit.
CNN 新闻： Here's one estimate by Dr. James Lawler at the University of Nebraska Medical Center: On March 5, he predicted that over the next two months, 4.8 million patients will be hospitalized in the US because of the coronavirus -- including 1.9 million stays in the intensive care unit. nevergetlost 发表于 3/14/2020 11:04:00 AM
A simple calculation below:
Assumption: all the recovered patients have effective antibodies
P: percentage of the population infected
pd: percentage of death among the infected
pd=3% to 4% (source: https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200306-sitrep-46-covid-19.pdf)
R0: reproduction number (the number of secondary infections generated from one infected individual)
R0=2 to 2.5 (source: https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200306-sitrep-46-covid-19.pdf)
The surviving population is [(1-P)+P(1-pd)].
To have herd immunity, we need the infection to slow down among non-infected people, so
{(1-P) / [(1-P)+P(1-pd)]} * R0 < 1
Thus:
P > (R0 - 1)/(R0 - pd)
When R0=2, pd=3%, we have P>50.76%
When R0=2, pd=4%, we have P>51.02%
When R0=2.5, pd=3%, we have P>60.73%
When R0=2.5, pd=4%, we have P>60.98%
Hence, the conclusion that 60% infection is needed for the herd immunity can be made by
R0=2.5, pd=3% to 4%.
What if R0=3.77? (https://www.medrxiv.org/content/10.1101/2020.02.10.20021675v2)
Then P>74.06% when pd=3%
P>74.25% when pd=4%
以上。Q.E.D.
看样子除了英国以外的欧美国家普遍认为，
1.现有条件无法改变感染总人数
2.快速感染会带来医疗资源挤兑和医护人员感染，大幅提高死亡率和其他疾病死亡率
3.关学校，取消大型集会，wfh可以拖延感染时间，避免挤兑
4.运气好的话，夏天可能消退。不然就等疫苗。这样最后感染总人数也可以减少
英国的脑回路奇特，他们似乎不认同上面的2，3，4点，采取平躺等死的状态。和中国处于两个极端。
他们的前提假设和其他国家不同。
武汉感染率距离群体免疫还差几百万人。
中英现在是两个极端。其他主要国家都在两者之间的不同位置。前所未有的浩大社会实验。
不停学校，不禁集会，这不是缓慢了
不是吧，这次禁航没禁UK诶，又是个大bug?!
刚禁了UK
https://www.bbc.com/news/world-us-canada-51891662