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Year on year risk
1. Pick an area with good covid stats. The google data on cases/hospitalizations/icu/deaths will do
2. Compare the stats for each with the numbers exactly one year ago. You may be surprised to find that unless the country is Qatar, every number will be worse than year on year. Including hospitalizations, icu and deaths
Like other respiratory viruses, SARS-Cov-2 is seasonal. You may recall that last year around this time, Florida and Texas had big waves before the north. And America had a big wave before Europe. Europe declared victory late summer 2020.
This is a surprising conclusion. Going into winter we appear to be in a worse position compared to last year.
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Relative vs. Absolute Risk of severe disease post vaccine
Here’s another exercise. Most reading this are likely vaccinated, as am I. You surely read that this vaccination has ~95% efficacy against severe disease. Great! I’ll take those odds. But what do they mean in absolute risk terms?
Let’s say that last year your local area had 1,000 cases a day, and had the wild type variant. At that level you had a certain risk tolerance. Now, relative to unvaccinated you back then, you have a 20x lower risk. But, it is 2021:
1. Delta seems to have a 2x odds ratio for hospitalization (source below). Oops. Your absolute risk reduction is only 10x.
2. Your local area has more cases now. See the first exercise. So if your area has 5x more cases, a typical multiple, then your absolute risk reduction for severe disease compared to same time last year is only 2x less. Oops.
Now, your peak risk will probably stay lower, as in a lot of places it is implausible that peak caseloads will hit 5x their peak loads. Among other things, ICU capacity would break before then. But this exercise is still valueable, as the merely relative protection of vaccination is unintuitive.
Oh, and the risk of an unvaccinated person compared to same time last year? 10x more! That preserves 95% efficacy.
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No one knows the future. Maybe these waves all peak, we hit the happy land of immunity as a herd, and we have a normal future.
But I say it is futility to declare victory over a respiratory pathogen until your country makes it through at least one winter with the level of restrictions you’d like. Summer is easy mode.
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Sources:
1. Delta hospitalization. This is actually relative to alpha, which may itself have had a higher hospitalization odds ratio relative to wild type: https://www.cidrap.umn.edu/news-perspective/2021/08/sars-cov...
2. Country stats. For quickly checking a country, google is fastest. But they generally pull from our world in data, which is the best aggregator: https://ourworldindata.org/coronavirus