Immunogenicity in monkeys of two polio type 3 seed viruses (SO + 2 and SOR + 1) presently used for production of oral polio vaccine.

Rhesus monkeys were immunized orally and intramuscularly with polio type 3 seed viruses (SO + 2 and SOR + 1). No immune response was detected after oral feeding. Geometric mean titres of 891.4 and 237.02 were obtained after intramuscular administration of six and eight doses of SO + 2 and SOR + 1 respectively. All the monkeys immunized with SO + 2 and SOR + 1 were positive for antibodies after third and fifth dose respectively. High antibody titre (1:1024) was reached in 80 per cent monkeys after sixth dose with SO + 2 whereas this antibody titre was obtained in 20 per cent monkeys after eight doses of SOR + 1. SOR + 1 was found to be a poor immunogen as compared to SO + 2 as it had produced low titre antibody response in monkeys even after administration of eight doses.