Sequential Use of Inactivated Poliovirus Vaccine followed by Oral Poliovirus Vaccine in Oman

Seroprevalence and geometric mean titers (GMTs) were compared at 6 and 10 months after vaccination with monovalent type 1 oral poliovirus vaccine (OPV) at 6 months and trivalent OPV at 7 and 9 months. Group 1 had received 4 doses of OPV, group 2 OPV at birth and 3 doses of OPV and inactivated poliovirus vaccine (IPV), and group 3 placebo at birth and 3 doses of IPV. A total of 547 infants completed the study. At 10 months, seroprevalence to poliovirus type 1 was 98%, 99%, and 98% in groups 1, 2, and 3; 100%, 100%, and 98% to poliovirus type 2; and 80%, 96%, and 91% to poliovirus type 3. Differences in seroprevalence among the groups were significant for poliovirus type 3 (P < .001). Between 6 and 10 months, significant increases in seroprevalence and GMTs occurred for poliovirus type 1 but not for types 2 and 3. Two OPV doses following 3 IPV doses did not significantly increase seroprevalence or raise GMTs for poliovirus types 2 and 3; however, significant increases were found for poliovirus type 1, which may have benefitted from monovalent type 1 administration.