On the relation between $U_q(\widehat{sl(2)})$ vertex operators and   $q$-zonal functions
  We show how the states constructed from the action of the modes of bosonized vertex operators, that intertwine $U_q(\widehat{sl(2)})$ modules, are related to $q$-zonal functions. 
A.H. Bougourzi and L. Vinet