We calculate the complete O (α2) initial state radiation corrections to e+e- annihilation into a neutral vector boson in a direct analytic computation without any approximation. The corrections are represented in terms of iterated incomplete (elliptic) integrals over alphabets of square-root valued letters. Performing the limit s ≫ me2 , we find discrepancies with the earlier results of Ref.  and confirm results obtained in Ref.  where the effective method of massive operator matrix elements has been used, which works for all but the power corrections in me2 / s. In this way, we also confirm the validity of the factorization of massive partons in the Drell-Yan process to O (α2). We add non-logarithmic terms at O (α2) which have not been considered in previous calculations. The final results in the limit s ≫ me2 can be given in terms of Nielsen integrals.