Regarding the flu shot: If you're at risk of not surviving the flu because your immune system is weakened, you might also not be gaining much protection from the flu shot, even in years where they got lucky with the target selection. But those same people *do* benefit if the healthy people around them are less likely to infect them. So you'd have to compare death rates at nursing homes where the staff is vaccinated vs not vaccinated. Might be tricky to get an IRB to sign off on that study though 😬

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