Information from The University of Iowa Hospitals & Clinics on COVID-19 vaccine boosters for the immunocompromised is here.
There is a meeting of the Advisory Committee on Immunization Practices (ACIP) scheduled for August 30, 2021 to discuss COVID-19 vaccine boosters. It looks like it was originally scheduled for August 24, 2021 but was rescheduled. This link to the Federal Register announcement identifies the matters to be considered (booster doses) of the meeting although the date for the meeting had not been updated at the time I wrote this post. Further ACIP meeting information is here.