“Can I renew an investigator-initiated R21 grant?”

Whether you can renew a grant is determined by the funding opportunity announcement (FOA) through which you apply, rather than the grant’s activity code. Check whether “Renewal” is listed under “Application Types Allowed” in Section II. Award Information of a given FOA.

That said, there are no active R21 FOAs on which NIAID is participating that allow a renewal application, including NIH Exploratory/Developmental Research Grant Program (Parent R21, Clinical Trial Not Allowed).