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trvrb's profile
Trevor Bedford
Trevor Bedford
Trevor Bedford
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@trvrb

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Trevor BedfordVerified account

@trvrb

Scientist @fredhutch, studying viruses, evolution and immunity. Collection of #COVID19 threads here: https://bedford.io/misc/twitter/ 

Seattle, WA
bedford.io
Joined December 2010

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    1. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      However, even when the entire population of a region has immunity through infection or vaccination, there may still be significant circulation of the virus due to waning immunity and viral evolution. 4/17

      3 replies 68 retweets 466 likes
      Show this thread
    2. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      As an example, seasonal influenza is an endemic respiratory virus and basically everyone over the age of ~3 will have immunity to it. However, despite this immunity, influenza infects ~10% of the adult population each year and causes perhaps 30k deaths per year in the US. 5/17

      5 replies 58 retweets 451 likes
      Show this thread
    3. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      Broadly, I expect the eventual endemic state of COVID to be similar with substantial circulation but reduced disease burden relative to the pandemic state. The key parameters here include: 1. R0 2. Waning immunity 3. Antigenic drift 4. Infection to fatality rate (IFR) 6/17

      11 replies 39 retweets 414 likes
      Show this thread
    4. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      R0 is the average number of secondary infections in a fully naive population. R0 of seasonal flu is around 2. R0 of Wuhan-like SARS-CoV-2 was around 3 and with Delta it's now perhaps 5 or 6. Higher R0 should correspond to greater circulation all other things being equal. 7/17

      8 replies 31 retweets 336 likes
      Show this thread
    5. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      Waning immunity is a bit more of an open question. Although, other seasonal coronaviruses appear to cause reinfections every ~3 years (https://www.nature.com/articles/s41591-020-1083-1 …), it's hard to completely extrapolate from these viruses to SARS-like coronaviruses. 8/17

      7 replies 32 retweets 335 likes
      Show this thread
    6. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      Trevor Bedford Retweeted Trevor Bedford

      But based on what we've observed with waning immunity to infection in SARS-CoV-2 (https://twitter.com/trvrb/status/1432725268658106376 …), I think it's safe to conclude there will be at least some waning of immunity to infection season-to-season in endemic state. 9/17

      Trevor Bedford added,

      Trevor BedfordVerified account @trvrb
      Importantly, @IsraelMOH observes a large difference between symptomatic illness and hospitalization, where protection against symptomatic illness waned, while protection against hospitalization remained robust (figure from slide deck https://www.gov.il/BlobFolder/reports/vaccine-efficacy-safety-follow-up-committee/he/files_publications_corona_two-dose-vaccination-data.pdf …). 10/14 pic.twitter.com/tgg3oOcfa8
      Show this thread
      5 replies 39 retweets 353 likes
      Show this thread
    7. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      Trevor Bedford Retweeted Trevor Bedford

      Although so far there's been relatively little antigenic drift in SARS-CoV-2, we've seen rapid adaptive evolution in the S1 domain of spike protein as selection pressure has driven increased transmissibility (https://twitter.com/trvrb/status/1437519286537318400 …). 10/17

      Trevor Bedford added,

      Trevor BedfordVerified account @trvrb
      Focusing on S1, we calculate a common metric called dN/dS that compares nonsynonymous mutations to synonymous mutations. We find that dN/dS in S1 increases through time during the pandemic with the most recent timepoint showing dN/dS of ~2.1. 6/12 pic.twitter.com/BPIK66a3EK
      Show this thread
      5 replies 31 retweets 283 likes
      Show this thread
    8. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      Given the early emergence of partial immune escape in the Beta, Gamma and Mu variants and given the spike protein's observed degree of adaptability, I would suspect that when selection pivots to be primarily immune driven we'll see steady antigenic drift. 11/17

      6 replies 35 retweets 327 likes
      Show this thread
    9. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      Recent adaptive evolution has been occurring at a significantly faster rate than H3N2 influenza, but my median scenario would be that with switch to endemicity, we see sustained antigenic evolution at a similar pace to influenza H3N2. 12/17

      4 replies 30 retweets 296 likes
      Show this thread
    10. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      High R0, waning immunity and antigenic drift together suggest substantial seasonal circulation with a speculative guess of 20% or 30% of the population infected each year (often referred to as the "attack rate"). This is higher than flu due to R0 of ~6 rather than ~2. 13/17

      14 replies 87 retweets 479 likes
      Show this thread
      Trevor Bedford‏Verified account @trvrb 13 Oct 2021

      At endemicity, circulation does not necessarily translate to disease burden. Based on robust vaccine effectiveness against severe outcomes, my speculative guess would be that infection to fatality rate (IFR) drops 10-fold from its original ~0.6% to a flu-like ~0.06%. 14/17

      7:42 AM - 13 Oct 2021
      • 78 Retweets
      • 467 Likes
      • 🔥 Jacob 🦊 Klee 🏳️‍🌈 thwh✍...😷 D-Bistoli (II) CCPandemic Connoisseur of Fine Internets Miguelito Cry for the Earth JudyM Just (Mildly) Curious
      20 replies 78 retweets 467 likes
        1. New conversation
        2. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

          Together, this would suggest perhaps 40k or 100k deaths per year in the US from COVID at endemic state. Most infections would be relatively mild (just like flu), but there's enough of them that even a small fraction of severe outcomes add up. 15/17

          20 replies 121 retweets 555 likes
          Show this thread
        3. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

          100k deaths would be 30% attack rate with 0.1% IFR, while 40k deaths would be 20% attack rate with 0.06% IFR. In general, like with seasonal flu I would expect significant season-to-season variability. 16/17

          15 replies 53 retweets 408 likes
          Show this thread
        4. Trevor Bedford‏Verified account @trvrb 13 Oct 2021

          This is not cancer or heart disease, but it's still a substantial public health burden. That said, yearly boosters just like flu vaccine, therapeutics like molnupiravir, improved ventilation and rapid testing can all contribute to reducing this ongoing burden. 17/17

          97 replies 122 retweets 1,099 likes
          Show this thread
        5. End of conversation
        1. New conversation
        2. Nafnlaus‏ @enn_nafnlaus 13 Oct 2021
          Replying to @trvrb

          Most studies pin Delta at 2+x higher IFR than Alpha. Now we've been countering this with vaccination and improved treatment, but starting with an artificially biases the comparison.

          1 reply 0 retweets 3 likes
        3. Trevor Bedford‏Verified account @trvrb 13 Oct 2021
          Replying to @enn_nafnlaus

          I'm very familiar with increased severity of Delta (https://bedford.io/papers/paredes-sarscov2-variant-outcomes/ …), but fair point. Eventual IFR is the biggest unknown to me in this list of 4 parameters.

          2 replies 1 retweet 15 likes
        4. Show replies
        1. New conversation
        2. Peter Ellis‏ @pjie2 13 Oct 2021
          Replying to @trvrb

          0.6% was for the original Wuhan version though - Alpha and the Delta increased this quite significantly, potentially as much as two fold.

          1 reply 0 retweets 7 likes
        3. Peter Ellis‏ @pjie2 13 Oct 2021
          Replying to @pjie2 @trvrb

          The age-specific IFR for repeat infections is something we URGENTLY need more data on. I fear it could end up over 0.1%, i.e. both more infectious and more lethal than seasonal flu.

          1 reply 1 retweet 10 likes
        4. Show replies
        1. New conversation
        2. Andreas Backhaus‏ @AndreasShrugged 13 Oct 2021
          Replying to @trvrb

          This drop would be driven entirely by immunity, as far as I understand. Do you see any likelihood that SARS2 might evolve into a variant that is less fatal to humans?

          2 replies 1 retweet 10 likes
        3. Show replies
        1. New conversation
        2. Anthony J Leonardi, PhD, MS‏ @fitterhappierAJ 13 Oct 2021
          Replying to @trvrb

          I don't see this happening with a superantigenic virus. I disagree with your projection and point to recent data from Iran.

          10 replies 6 retweets 77 likes
        3. Dr Matt Prescott‏ @mattprescott 13 Oct 2021
          Replying to @fitterhappierAJ @trvrb

          I see no reason to assume positive outcomes

          1 reply 0 retweets 17 likes
        4. Show replies

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