Why a SARS-CoV-2 variant that's 50% more transmissible would in general be a much bigger problem than a variant that's 50% more deadly. A short thread... 1/
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As an example, suppose current R=1.1, infection fatality risk is 0.8%, generation time is 6 days, and 10k people infected (plausible for many European cities recently). So we'd expect 10000 x 1.1^5 x 0.8% = 129 eventual new fatalities after a month of spread... 2/
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What happens if fatality risk increases by 50%? By above, we'd expect 10000 x 1.1^5 x (0.8% x 1.5) = 193 new fatalities. 3/

2:40 PM · Dec 28, 2020

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Now suppose transmissibility increases by 50%. By above, we'd expect 10000 x (1.1 x 1.5)^5 x 0.8% = 978 eventual new fatalities after a month of spread. 4/
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The above is just an illustrative example, but the key message: an increase in something that grows exponentially (i.e. transmission) can have far more effect than the same proportional increase in something that just scales an outcome (i.e. severity). 5/5
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Replying to @AdamJKucharski
I got seriousness of this day one. Anyone w/basic math skills should be able 2 determine if we have 50% more cases flooding ERs @ same time, that collapses our medical infrastructure even faster. This strain is not deadlier just spreads faster. Our hospitals can’t handle this.
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Replying to @AdamJKucharski
Thanks for that. I intuitively figured but appreciate you laying it out. Why to the 5th power?
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Replying to @AdamJKucharski
Makes a lot of sense. The virus cannot grow outside host. By increasing fatalities, it reduces host numbers. From evolution perspective, such a strain may not survive for long. On other hand, a strain that is more contagious has better chances to survive.
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