Study: Pfizer vaccine 88 percent effective against delta variant

[Ms. Toad]

29. Vaccine effectiveness compares vaccinated cases to unvaccinated cases.

So 12% less effective means that for every 100 cases in an unvaccinated population we can expect to see 12 cases in a vaccinated population wtih similar exposure.

(This is the opposite calculation error of what many are making with the LA data - in which a snapsnot in time is being used to assert that the chance of death is only .0027%.)

So while it is true that there are more breakthrough cases because there are more vaccinated individuals, the calcultaion is a bit more complicated to determine if the increased vaccination accounts for all of the increased breakthrough cases.