The time kinetics of poliovirus and secretory IgA (sIgA) antibody titers were examined in fecal samples from four vaccinees immunized with two doses of trivalent oral polio vaccine (TOPV) from 1996 to 2000. Poliovirus types 1 and 2 multiplied in the human intestine after the first vaccination, and poliovirus type 3 multiplied after the second vaccination. Additionally, poliovirus type 3 multiplied for several days in two cases after the first vaccination, and poliovirus types 1 and 2 multipliedfor before and after a week in one case after the second vaccination. Poliovirus type 2 multiplied most efficiently in the human intestine and stimulated the sIgA antibody response. The sIgA antibody titers are required to be≥1: 4 for poliovirus types 1 and 3, and≥1: 8 for poliovirus type 2 in 10% fecal suspension for adequate TOPV protection against reinfection. Serum neutralizing antibody titers against poliovirus type 3 were 1: 6 and 1: 8 for the shorter periods of 16 and 13 days, respectively, and 1: 60 and 1: 45 for 36 days in multiplication of poliovirus type 3 after the second vaccination. For double infection of poliovirus types 1 and 2, only the higher titers were obtained.
These results suggest that poliovirus multiplication induces the sIgA antibody inthe human intestine and the induced sIgA antibody defends the subject from poliovirus infection, and that the duration and the amount of virus multiplication tend to correlate with the levels of the serum neutralizing antibody titers.