3 ms·
Imagine a study where half gets vax and half doesn't. If population is pristine at outset at end of study VE is 1-ratio between people who get COVID in the two
by avsteele 5y ago
Imagine a study where half gets vax and half doesn't. If population is pristine at outset at end of study VE is 1-ratio between people who get COVID in the two arms.
Now, if there is any prior exposure to the disease among participants (this isn't always known, esp. for something like COVID), and if there is any natural immunity that accrues, this will pull that ratio towards 1 (VE=0)