an N-acetyl-alpha-neuraminyl-(2->3)-beta-D-galactosyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + CMP-N-acetyl-beta-neuraminate = an alpha-Neu5Ac-(2->8)-alpha-Neu5Ac-(2->3)-beta-D-Gal-(1->4)-beta-D-GlcNAc derivative + CMP + H(+) — reaction