It’s probably already going on off label.
“No scientific data to support it.” Why? Because they haven’t run the study? Or, because the study showed it does not give more protection? Two very different things.
I think third doses should be available to Americans who likely did not spike antibodies and would benefit from a third dose. We need to do this study! The people most likely not to develop strong antibodies are the same people most likely to get severe disease. These Americans are in essence still not vaccinated without the third shot.
A German study showed only 70% of people over age 80 got immunity from the two shots. 30% resulted in no immunity.
Israel is recommending a third shot for Pfizer for people over age 60. I assume they have some data, but I would like to know exactly what the data is. Is it actually producing immunity, or they just hope so.
In America it is more important everyone get their first set of shots than the booster. As far as the world, we should coordinate with other countries, and it seems logical to me that other countries get first doses before we consider giving everyone a third shot in America.
However, some of it can be happening simultaneously obviously.