Five-loop vacuum polarization in pQCD: O(mq2αs4nf2) contribution

We present the analytical calculation of the contribution of order mq2αs4nf2 to the absorptive part of the vacuum polarization function of vector currents. This term constitutes an important gauge-invariant part of the full O(mq2αs4) correction to the total cross-section of e+e− annihilation into hadrons. The results are compared to predictions following from various optimization schemes.