Since everyone's talking about herd immunity in the United States at the moment, I thought I'd quickly run some rough calculations of the number of deaths required to get to the herd immunity threshold for COVID-19 in the U.S.
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The age-stratified IFRs that I'll use are from my and co-authors paper available here:https://www.medrxiv.org/content/10.1101/2020.07.23.20160895v4 …
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Taking the ages/population figures from the US census, and the midpoint of the age brackets as the mean IFR for that group, you get this breakdownpic.twitter.com/CZS0k0dXCB
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Using our bog-standard Herd Immunity Threshold calculation, which requires 70% of people to become infected, we get just over 3 million deaths required to reach herd immunitypic.twitter.com/UgiZSL8SYO
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Now, this requires something that we actually don't see - for the older age group to be infected as often as the young This isn't very common for COVID-19
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If we instead assume that people >65 are infected a bit less, and those >80 are infected a LOT less (in line with current trends), we get a perhaps more realistic figure of 1.76 million deaths in the U.S. before herd immunitypic.twitter.com/tSpxwwko4X
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"But wait!", I hear some people cry, "The herd immunity threshold is lower than 70%!" Well, maybe. If we reduce the threshold to 20%, which is one of the lowest figures proposed, we see either 880,000 or 504,000 deaths depending on who gets infectedpic.twitter.com/uciCBcJUiL
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Not necessarily. Deaths have a very long tail (i.e. some people don't die for a long time) so even if the new cases stopped today you'd expect to see deaths go quite a bit over the next month or two
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