Well that would be Miloslav Kabeláč: Symphony No. 5 in B flat minor, "Dramatic", for soprano without text, and orchestra, op. 41 (1960), would not it?
That is correct and the Member gains four hundred points. This
soprano is an unusual idea but seems quite effective in a way, which is not of course to say that we would wish every symphonist to incorporate a
vocalise from beginning to end.
Having said that (that symphonies with sopranos are so unusual) we seem over the past few days to be encountering nothing
but symphonies with sopranos; specifically Alfven's
Fourth, "From the Outskirts of the Archipelago", with soprano and tenor double vocalise, which dates from 1919, and Nystroem's
Third, "Sinfonia del Mare", again with soprano, from 1948 - both it will be noted from well before the Kabeláč.