The 25th Amendment says that the Vice-President, in conjunction with half of the fifteen executive department heads, can declare the President unfit to discharge his duties. Presently only two of the fifteen departments have confirmed heads (Defense and Homeland Security). The other thirteen are headed by acting secretaries (or equivalent).
If the Vice President were to invoke the 25th Amendment, who would actually be required to support his declaration of the President's unfitness? Would eight acting secretaries be sufficient? Or do they count? Would only one of the two confirmed secretaries be sufficient? Or would he have to actually wait until there are at least eight confirmed secretaries?