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/
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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

2:40 PM · Dec 28, 2020

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Replying to @AdamJKucharski
Do we have data on the fatality risk of this strain? Is it more contagious but less deadly? Just as deadly? Too soon to tell?
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Holding everything else constant, per infection mortality risk might be equally, but an increased strain on medical infrastructure cased on increasing caseloads might result in saturation at hospitals which would reduce access to services and thus increase morality.
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Replying to @AdamJKucharski
Sooo covid is here to stay?
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Replying to @AdamJKucharski
Superbly expressed. Also, saturation of hospitals would be more likely to occur and on a more widespread basis, reducing access to care and thus increasing morality for not only COVID-19 but for all those requiring critical care.
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Viruses R no-more immune 2 rules of natural selection than other life on Earth: if they mutate into too-lethal of a variant, they end up killing their hosts before their progeny can be transmitted to their next host (victim). Too-lethal variants sign their own death warrants.
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Replying to @AdamJKucharski
You get more deaths more quickly with the one more contagious, but more deaths *overall, long term* with the one that's more deadly.
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Given increasing access to highly effective vaccines, in a real world scenario, the curves would likely not intersect let alone crossover.
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Replying to @AdamJKucharski
Why does the equation use R^5 and not R to determine spread?
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1 month of spread; generation time 6 days. Therefore 5 x 6 days = 30 days = 1 month.
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Replying to @AdamJKucharski
Also should be pointed out that the more cases there are, the more chances for a new variation or mutation that can be even worse. We really need to get this under control.
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