The FDA said while some observational studies do show Pfizer's vaccine has waning protection against the Delta (B1617.2) variant, other studies do not.

Pfizer's mRNA-based vaccine is the only FDA-approved COVID-19 vaccine for use in the United States, and the company's application is for a third booster dose to be given 6 months after the initial two-dose series. Currently the FDA has authorized the emergency use of a third dose of Pfizer for immunocompromised Americans.

"Overall, data indicate that currently US-licensed or authorized COVID-19 vaccines still afford protection against severe COVID-19 disease and death in the United States. There are many potentially relevant studies, but FDA has not independently reviewed or verified the underlying data or their conclusions," the report reads.