My understanding is that a 3rd dose today is the same as previous doses. Trials are underway to be more effective against newer variants.
This is from July 8th
https://investors.biontech.de/news-releases/news-release-details/pfizer-and-biontech-provide-update-booster-program-light-delta
Pfizer and BioNTech have seen encouraging data in the ongoing booster trial of a third dose of the current BNT162b2 vaccine. Initial data from the study demonstrate that a booster dose given 6 months after the second dose has a consistent tolerability profile while eliciting high neutralization titers against the wild type and the Beta variant, which are 5 to 10 times higher than after two primary doses.
While Pfizer and BioNTech believe a third dose of BNT162b2 has the potential to preserve the highest levels of protective efficacy against all currently tested variants including Delta, the companies are remaining vigilant and are developing an updated version of the Pfizer-BioNTech COVID-19 vaccine that targets the full spike protein of the Delta variant. The first batch of the mRNA for the trial has already been manufactured at BioNTech’s facility in Mainz, Germany. The Companies anticipate the clinical studies to begin in August, subject to regulatory approvals.