With data that has emerged in the last week, I'm now 80-90% convinced that infections by the UK variant virus (Pangolin lineage B.1.1.7, @nextstrain clade 20B/501Y.V1) result in, on average, more onward infections, ie are more transmissible. 1/10https://twitter.com/trvrb/status/1341446447045087232 …
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My thinking primarily comes from three data points: 1. rapid increase in frequency of variant over wildtype 2. higher secondary attack rate of variant than wildtype 3. increased viral loads of variant over wildtype as measured by Ct 2/10
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For point 1 (increase in frequency) we have pretty much the same data as of a week ago, where we see increasing frequency of variant over wildtype across the UK. This can be readily seen in this analysis by
@TWenseleers. 3/10 https://twitter.com/TWenseleers/status/1343575693544796160 …pic.twitter.com/lWu5kTDWgo
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For point 2 (secondary attack rate), we have new data from the second @PHE_uk technical report (https://www.gov.uk/government/publications/investigation-of-novel-sars-cov-2-variant-variant-of-concern-20201201 …) where a matched cohort study was conducting comparing 1769 wildtype cases and 1769 matched variant cases. 4/10
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By integrating contact tracing data @PHE_uk was able to compare secondary attack rate between wildtype cases and variant cases, where ~10% of contacts of wildtype cases go on to be detected as COVID+ compared to ~15% of contacts of variant cases. 5/10pic.twitter.com/sLSVcIzVpT
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Both increase in frequency and secondary attack rate indicate essentially the same quantity, which is the number of secondary infections left by a primary infection, ie R, and tells us that realized transmission rate is likely higher in variant than wildtype infections. 6/10
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For point 3 (viral load), we have new data as reported by Michael Kidd,
@alanmcn1 et al (https://www.medrxiv.org/content/10.1101/2020.12.24.20248834v1 …) that shows that variant cases (as identified by S dropout) have Ct values ~4 units lower than wildtype cases. 7/10pic.twitter.com/ZIQQH1NFZS
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This translates to an estimated 10 to 100-fold increase in average viral load of variant cases. This gives a hypothesized mechanism for increased transmissibility, ie individuals infected by the variant will on average expel more virus and be consequently more infectious. 8/10
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this seemingly conflicts with reports that viral load is correlated with severity, yet at the same time this variant is supposedly not more severe? there are probably many subtleties...
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Replying to @DanielleFong @trvrb
I'm confused on this point as well. Everything I've heard, higher load=more severe
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