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by maxerickson
2095 days ago
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The bullshit is that Sweden has reached herd immunity. People in this thread clearly understand that there is a certain level of population immunity where R₀ goes below 1, they are arguing that Sweden has not reached the point where things are 'normal' and R₀=1, they are taking various measures to control the virus, and the rate of spread will go up if they relax those measures. That's not unqualified 'herd immunity', it's not even close. (https://www.businessinsider.com/sweden-decline-coronavirus-d... discusses some of the things that Sweden is doing, which are indeed largely voluntary) |
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R, or as I prefer to call it, R(t), is the number that factors in how many have immunity. So you mean herd immunity is when R(t) < 1.
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Anyway, I was having trouble understanding exactly what you were saying about Sweden, but to be clear, Sweden has hit herd immunity, unless you think that the utter absence of COVID mortality at this point is due to seasonality.
What you need to understand is that simplistic models view the population as homogenous, both in terms of mixing (social connections) AND susceptibility/transmissibility. Neither are true. Essentially, the people who tend to get infected sooner in the pandemic are the ones who tend to spread more, so the first, say, 10% of antibody prevalence is worth a lot more than the next 10%.
There's also the presence of pre-existing T-cell cross-reactivity; exposure to other hCoVs is protective against SARS-2. It seems that it does not protect infection, but it does make the disease course a non-issue: this probably explains the high degree of asymptomatic infection (with part of it just being explained as an artifact of the PCR cycle threshold fuckery). Technically these findings are already implicitly factored into the estimates we have for R_0, etc. (BTW, initial studies were claiming R_0 of 5.2, 5.5, etc, but now with more data it seems it's around 2, give or take)
Many, and I am in this category, believe that the true herd immunity threshold is somewhere around 20% of the population. That explains what we've seen in places like New York, Sweden, etc. This is lower than what the classic herd immunity formula would predict, because that formula does not account for a non-homogenously-mixed population (as I mentioned earlier), nor does it account for certain individuals having an innate genetic resistance that makes it less likely that they get infected.