Sera collected before introduction of contaminated polio vaccine contain antibodies against SV40.

Anti-SV40 IgG antibodies were found by ELISA test in 6 out of 51 sera collected in 1952, i.e. before introduction of the polio vaccine. This indicates that the presence of SV40 in the human population whose footprints can be found in a fraction of human cerebral tumours need not be the consequence of contamination of early batches of polio vaccine with SV40.