Mucosal Immunity to Poliovirus following Administration of Inactivated Polio Vaccine

Abstract

The studies reported here were carried out to evaluate mucosal immunity to a single dose of IPV in children who had been immunized with at least 5 doses of OPV, the last dose at least 6 months previously and to evaluate available laboratory methods for assessment of virus shedding. The following are the important findings of the study: 1. A single dose of IPV in previously OPV immunized children led to a substantial increase in the serum neutralizing antibody titres (all three serotypes) in comparison to children who received a dose of bOPV. 2. A single dose of IPV given to children who were previously primed with OPV resulted in strong mucosal immunity as evidenced by a substantial reduction in shedding on day 7 of challenge with bOPV (serotype 1 and 3). In contrast, a dose of bOPV did not significantly reduce the proportion of children shedding vaccine poliovirus after a subsequent challenge, although the amount of virus shed was less. 3. The effect of a single dose of IPV on poliovirus shedding was no longer significant on days 14 and 21 after challenge. This finding suggests that although a booster dose of IPV reduces the amount of poliovirus replication at the peak of shedding (day 7), it might allow a lower level of replication that can be detected at a later time. 4. Of samples positive by PCR for a single serotype (1 or 3), 87-89% were also positive by culture, indicating good correlation of findings. A higher threshold for virus copy number also correlated well with virus culture. 5. There was good correlation between singleplex real-time PCR and the one step multiplex realtime PCR in the detection of poliovirus from stool samples. A single dose of IPV offered substantial benefit in comparison to further doses of OPV in boosting humoral and intestinal immunity in children previously primed with live poliovirus. Quantitative molecular methods offer substantial benefits in terms of ease of testing and use of resources. These findings support for an expanded role for IPV in the polio end-game strategy.