Some single dose vials (SDV) contain more than the recommended dosage of the vaccine. Should we administer the recommended dose of the vaccine, or the entire contents of the vial even if it contains more than the recommended dose?

In general the entire volume should be used even if it is a little more than 0.5 mL. Discarding the excess vaccine is not required or recommended. An exception to this is recombinant zoster vaccine (RZV; Shingrix, GSK). The RZV adjuvant solution may contain up to 0.75 mL of liquid. The entire volume of the adjuvant solution should be withdrawn and used to reconstitute the lyophilized vaccine. After mixing, withdraw the recommended dose of 0.5 mL. Any reconstituted vaccine left in the vial should be discarded.