3) Lower herd immunity threshold (HIT) Infections are now declining in almost all heavily-impacted states, despite no clear policy interventions. Estimating the HIT based on the current effective reproduction numbers results in a ~10-35% effective HIT. (Formula: HIT = 1-1/Rt)
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From my understanding, the herd immunity threshold of SARS-CoV-19 is still 60-80% given an R0 of 2.5-3. So early reports are not "wrong". It's just that the Rt is much lower now after reopening (1-1.5) due to changes in behavior/policy, and that results in a lower effective HIT.
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These are the best conclusions I have come up with after working with this data on a daily basis for the past 4 months. Full disclaimer: I am not an epidemiologist, so if anything I said is inaccurate, let me know and I will be happy to correct them.
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I tried to write the report in a way such that an average layperson who has been following COVID-19 can understand it. Before commenting, I encourage everyone to read the report first, particularly the "Disclaimers" section.
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As usual, the data and results of everything I presented are open-source: https://github.com/youyanggu/covid19_projections/tree/master/implied_ifr … You can find estimates of the true daily new infections, implied IFR, implied CFR, etc for every state and nationally. I aim to update this data daily.
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Summary: Good news: We are likely past the peak. Bad news: ~1,000 people are still dying every day and may remain at a high level for some time, esp with school reopenings & flu season coming up. Thanks for reading. I'll be going through the comments for feedback/suggestions.
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Youyang Gu Retweeted Wes Pegden
Addenum #1: I should clarify that the lower effective herd immunity threshold is due to the *current interventions & social distancing in place*. If those interventions are relaxed, we would go back to a higher HIT. Better insights on HIT by
@mgmgomes1:https://twitter.com/WesPegden/status/1287575304639315975 …Youyang Gu added,
Wes Pegden @WesPegden@mgmgomes1 and coauthors have a preprint out where they analyze the impact of models incorporating variability in exposure (contacts) or susceptibility on epidemic trajectories in several countries. Quick thread on this and recent reaction to it.
1/17
https://www.medrxiv.org/content/10.1101/2020.07.23.20160762v1.full.pdf …Show this thread12 replies 21 retweets 134 likesShow this thread -
Youyang Gu Retweeted Dan weinberger
Addenum #2: We only use reported deaths in our implied IFR calculations. But if states are underreporting deaths, then the implied IFR would be a lower bound on the true IFR.
@WeinbergerDan and his lab have been taking a deep dive into excess deaths:https://twitter.com/WeinbergerDan/status/1289255927732895750 …Youyang Gu added,
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Replying to @youyanggu @WeinbergerDan
I’m having a bit of a hard time with the concept of effective HIT. If citizens believe we have reached “herd immunity” then we might presume the behaviour goes back to baseline thereby reversing the HIT. Or am I missing something?
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@GidMK1 reply 0 retweets 0 likes
No I think that's a reasonable issue. If the HIT is lowered due to heterogeneity of exposure, then it can be raised again if that heterogeneity increases again. Can't assume that people's behaviour will maintain static patterns!
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