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Is the infection rate really the correct measurement here? It seems like that refers to a discrete period of time. But we have an endless supply of those periods of time. Eventually, without a vaccine, wouldn't we ultimately end up with roughly 60% infected or whatever the herd immunity threshold is? So, that would mean that for 1000 patients, 300 patients would benefit from a vaccine, which would make C 30% for the vaccine.


TBW: Nice comment. I haven't worked out the math behind this but my hunch is that the 50% effectiveness threshold is arrived at after further modeling of the community spread given a certain percent of immunity from the vaccines. Vaccination is always preferred to letting the virus spread through the community because each infection carries the risk of severe illness and death. We will also learn from the trials whether the 0.75% base infection rate is in the right ballpark (after writing this, I realize that they may be using the "detected" infection rate - really the case rate - because they are not testing 30,000 people every day to monitor the infection.)

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