The FDA application for boosters claims that efficacy against transmission for delta for persons vaccinated when the vaccine became generally available is now 4

The FDA application for boosters claims that efficacy against transmission for delta for persons vaccinated when the vaccine became generally available is now 42%. That isn't enough to drop Reff below 1 even with 100% vaccination-- in fact, it leaves delta with an Reff higher than the original L strain had absent vaccination.