Current prospects on covid-19 herd immunity

Herd immunity provides indirect protection to those who are not immune to the disease. Herd immunity requires that most of a population be immune - depending on how contagious an infection is, usually 70% to 90% of a population needs immunity to achieve herd immunity. 

Given that we don't have an effective vaccine against covid-19 virus, is it reasonable to try to achieve herd immunity against this virus? The short answer is no, but we could imagine trying. 

First consider how many people would die trying to achieve herd immunity. For now, we will ignore long-term complications for those who recover from severe illness. 

To gauge death rate, and we need accurate number of all dead and of all infected. With most countries including the USA, Italy, and China, we don't know the true extent of infection. The two most reliable cases are the cruise ship Diamond Princess (13 dead out of 712 infected = 1.8% death rate) and South Korea (256 dead out of 10810 infected = 2.4% death rate as of May 7). 

With South Korea, their confirmed cases should reasonably approximate the true number of infected. If confirmed cases are 75% of true infected, death rate would be 1.8%. Even if confirmed cases are ONLY half of true infected, death rate would be 1.2%.

There's also the preliminary antibody test results from New York, which indicates 20% infection rate in New York City and 12% statewide according to Governor Cuomo. There are many problems with using these numbers for getting the death rate - FWIW death rate is arguably 1% with these numbers.

For simplicity, I'll use a death rate of 1% - which is overly optimistic IMHO. I'll also use the low-end 70% immune to achieve herd immunity. 

For Sweden (10.23 million), 70% or over 7 million people need to be infected. At 1% death rate, 70,000 people would die. 

FWIW, Sweden has reported under 2700 dead so far. 

Can we do better? Maybe. Perhaps we should only infect the strongest. How does Swedish population look by age? 

Sweden (population 10.23 million) by age
age 0-14 17.5%
age 15-24 11.1%
age 25-54 39.4% -- 68.4% (0-54)
age 55-64 11.7%
age 65+ 20.4%

Maybe only people under 55 (or 56 or 57) could be infected to get to 70%. For now, assume that there is no dispensation for people with underlying conditions. Forget advocating testing this on some subpopulation first (e.g. those in jail, based on race, only Republicans or Democrats, etc.).

Younger people survive covid-19 better. Here are numbers from South Korea.

covid-19 death rate by age in South Korea
age 80+ 24.6%
age 70-79 10.7%
age 60-69 2.7%
age 50-59 0.77%
age 40-49 0.21%
age 30-39 0.17%

With the group under 55, death rate may be 0.3%. Heck - let's be really optimistic again and use 0.1%. Back to Sweden, 7 million infected leads to 7000 dead. 

Now there is the task of infecting 7 million while keeping the other 3 million safely sequestered.

How do you infect people? Start with one sick individual coughing on thousands of uninfected people a day? Spray people in enclosed chambers with lab-grown virus? How long would this take? Could all 7 million be infected at the same time? No. Heck - infecting 1 million at a time in a 1 week period would be a logistical nightmare. Even at this rate, it would take 7 weeks to infect 7 million people deliberately. 

When could the infected population get back to interact with the older sequestered population? Maybe 2 weeks for those with mild or no symptoms? If one million were infected now, maybe those one million could start helping out the older population of 3 million 2 weeks later? In this 'ideal' scenario, it could be 'completed' more or less after a bit over 2 months.

Now, step back and consider the whole endeavor in terms of your ideas of personal freedom and human rights. How does it compare to prolonged stay-at-home order? 

Also think about how this affects the USA (population 329 million) instead of Sweden. 

USA age demographics
24% age 0 to 18
9% age 19 to 25
12% age 26 to 34 -- 45% (0-34)
26% age 35 to 54 -- 71% (0-54)
13% age 55 to 64
16% age 65+

Death rate of 1% for 230 million (70%) means 2.3 million dead. Death rate of 0.1% selectively infecting those under 55 means 230,000 dead. Trying to consider which is better is painful and ultimately a futile exercise. Some people say one death is tragedy whereas one million deaths is just a number - well, it is one million tragedies. 

No one wants the covid-19 emergency to drag on for a long time. It is understandable that people want to get back to work and live more or less normally - the question is when. Many people may prefer to take their chances (Russian roulette). On the other hand, advocating for herd immunity against covid-19 without vaccines is monstrous. Having to argue against such herd immunity approach is absurd.