[ArkVark]

The simplest explanation for Madrid is that it locked down too early, and herd immunity (which seems to occur at about 20-25%, based on Antibody testing of New York and Sweden) was never reached.

Lockdown also seems to increase the threshold for herd immunity and increase deaths, by dramatically changing the demographics of who is infected. Without lockdown, the youngest and most mobile people are likely to be infected - with minimal/zero deaths since COVID mortality is incredibly age dependent.

Under lockdown, those people are at home and intermingling with family. The only 'social' activity is shopping for food, leading to an unnatural mingling of old and young.

I live in Ukraine which has masks and little else against COVID. In shopping centers particularly in the evenings there are essentially zero old people - they fear for their lives, as they should.

The most effective policy we could have adopted was 6AM-10AM public transport and shopping for the aged only, and everyone else from then on. Segregate the elderly population into the mornings and let the masses in in the afternoon. This might have required shifting school and work to later hours in the day for three months, which seems a minor inconvenience.

[michaelmrose]

Nobody credible believes 20-25% is a likely threshold for herd immunity. You cannot Realistically in America isolate the old from the young and if the young spread it like wildfire the old get sick.

Literally everything in your post is as poorly considered. It's important not to spread misinformation.

[T-hawk]

It's 20%-25% of currently detectable antibodies, coupled with another 20%-50% from prior coronaviruses or other cross-immunity. That's the important distinction. The sum approaches the 50%-70% needed for herd resistance based on 1-1/R0. That's the point of this article.

[michaelmrose]

A couple people suppose is not the same as proof

[millettjon]

See: https://www.news-medical.net/news/20200731/Research-suggests...

In addition to immunity based on T cells, the HIT depends on how individuals are networked. The original 60-70% estimates were based on 100% of people being vulnerable and also a random distribution of individuals interacting. In reality a small fraction of the population will have many interactions and once they become immune those transmission vectors away and the average R number drops. So based on the latest research plus observations of the worst hit places, 20-25% seems plausible.

[belltaco]

Why are you assuming young people don't live with old people? It's extremely common.

[gridlockd]

It's rather uncommon in most European countries:

https://ec.europa.eu/eurostat/documents/3433488/5579620/KS-S...

Looking at this data for the US, it could be a factor for COVID mortality being higher in minorities:

https://www.pewsocialtrends.org/2010/03/18/the-return-of-the...

[TheAlchemist]

Your data actually says the opposite for Europe - it's highly dependent of the country of course, but if you look at page 6, in Southern countries - Spain, Italy, you have >30% of old people living with larger family (columns 'living with partners plus others' and 'no partner, not living alone'). That comes out at <10% for Nordic countries (Finland, Sweden etc)

[gridlockd]

Three-generation house-holds or households where adult children live with their older parents are very uncommon in most, but not all, EU countries.

The numbers you cite are explained by old people living in retirement facilities or coliving arrangements, but that doesn't imply cohabitation with young people. Under these circumstances, special precautions can and must be taken.