The SO(4) symmetry of a sector of the QCD Hamiltonian is explored, adding to (2+1) flavor degrees of freedom. In spite of the complexity of the QCD spectrum at low energy,  the treatment of the QCD Hamiltonian in the SO(4) representation, including ground state correlations by means of the Random Phase Approximation, allow us to identify states which may be associated to physical pseudo-scalar and vector mesons, like $\eta$, $\eta'$, $K$, $\rho$, $\omega$, $\varphi$, as well as the pion ($\pi$).