Would getting 40 mcg (two x 20 mcg) booster dose of hep. b vaccine likely prolong surface antigenemia longer compared to receiving only 20 mcg?

Possibly: The incidence of hbsag positivity after hbv vaccination with recombinant hbsag is low and depends on the assay being used. In one study, 5% of vaccinated blood donors tested positive one day later using 20 mg dose but negative at 3 days. They cited one example of a 40 mg recipient that was positive at 5 days. The recommendation is to delay blood donation up to one week after hbv vaccination.