Immunogenicity and fecal poliovirus excretion in sequential use of inactivated and oral poliovirus vaccines.

BACKGROUND AND PURPOSE: Though inoculation with inactivated poliovirus vaccine (IPV) is advocated, sequential use of IPV and live oral poliovirus vaccines (OPV) has many advantages. This study aimed to define the immunogenicities of IPV and OPV in Taiwanese children after the use of a sequential schedule of IPV-OPV and also to determine whether prior IPV inoculation hampers the fecal passage of OPV. METHODS: Fifty-nine infants were recruited to receive IPV-OPV sequential vaccinations consisting of IPV given at the ages of 2 and 4 months and OPV given at the ages of 6 and 18 months. Blood samples were taken at ages 2, 6, 18, and 19 months for antibody determination, and stool samples were collected to isolate vaccine strains of poliovirus after the second dose of OPV, at the age of 18 months. RESULTS: None of the children had severe systemic or local reactions. Protective antibodies were detected in all infants at the age of 6 months, 2 months after the second IPV dose. The antibody titers were augmented at the age of 19 months, 1 month after the booster dose of OPV. Stool samples collected 7 days after the second dose of OPV yielded at least one type of poliovirus in 9 of 18 children. Analysis of stool samples revealed that poliovirus was excreted by the 28th day in only two of the children. CONCLUSIONS: Our study showed that both IPV and OPV exhibit immunogenicity in Taiwanese children. Side effects of an IPV-OPV sequential schedule were mild and infrequent. Viral shedding in stools after OPV vaccination was preserved in a substantial proportion of subjects. These findings suggest that this sequential vaccination schedule can maintain herd immunity.