Coronavirus - herd immunity

Herd immunity "is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, whether through previous infections or vaccination, thereby providing a measure of protection for individuals who are not immune. In a population in which a large proportion of individuals possess immunity, such people being unlikely to contribute to disease transmission, chains of infection are more likely to be disrupted, which either stops or slows the spread of disease. The greater the proportion of immune individuals in a community, the smaller the probability that non-immune individuals will come into contact with an infectious individual, helping to shield non-immune individuals from infection" (Wikipedia).

It's clear that herd immunity is effective when the already-immune portion of the herd is high, but has little effect when the already-immune portion of the herd is very low.  Amid all the panic, herd immunity has received little attention during the ongoing coronavirus pandemic. Given the newness of the virus, SARS-CoV-2, and no vaccine for it, the already-immune portion of any country's population is very low.

In this interview Professor Knut Wittkowski relies heavily on the idea of herd immunity to combat the coronavirus. He may be correct, but I didn't share his confidence. First, the already-immune portion of people is very low. Without vaccination, many, many people would have to become infected -- in a non-controlled way unlike vaccination -- to reach the critical mass for herd immunity to have much effect. Second, it seems he relied too much on mortality rates from the flu. The range of annual flu deaths is wide. He predicted the number of deaths in the USA will be in the low end of that range. Deaths from the SARS-CoV-2 being one cause already are near the high end of that range and will exceed it. Wittkowski emphasizes children becoming immune via exposure to SARS-CoV-2 without it being fatal (or even sickening). However, children ages 0-14 are only about 19% of the USA's population, with ages 0-18 about 24%. In summary, the downside of non-immune people being exposed to SARS-CoV-2 seems risky. He also relies on isolating the elderly, but there are many elderly living among the general population, not in nursing homes or assisted care residences. Of course, non-immune people avoiding exposure to the virus does not require the sort of massive lock-downs that have been implemented by governments.

These two articles #1, #2 reach the same conclusion about how lethal the virus is. The lack of a vaccine is likewise a weighty factor.

One country, Sweden, has relied on a herd immunity approach and no strict lock-down. Its neighbors Denmark, Finland, and Norway have kept reported infections and deaths lower, especially deaths (link). This article addresses Sweden's case somewhat favorably. This article addresses Sweden's case more negatively.