Discharge of functions of President
Section 146(3) · 1999 Constitution (2004 edition)
What Constitution says
(3) Where the office of Vice-President becomes vacant:- (a) by reason of death or resignation, impeachment, permanent incapacity or removal in accordance with section 143 or 144 of this Constitution; (b) by his assumption of the office of President in accordance with subsection (1) of this section; or (c) for any other reason, the President shall nominate and, with the approval of each House of the National Assembly, appoint a new Vice-President.
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 73–74. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections