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 va ccine (OPV) at 6 months and trivalent OPV at 7 and 9 months. Group 1 h ad received 4 doses of OPV, group 2 OPV at birth and 3 doses of OPV an d inactivated poliovirus vaccine (IPV), and group 3 placebo at birth a nd 3 doses of IPV, A total of 547 infants completed the study, At 10 m onths, seroprevalence to poliovirus type 1 was 98%, 99%, and 98% in gr oups 1, 2, and 3; 100%, 100%, and 98% to poliovirus type 2; and 80%, 9 6%, 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 occur red for poliovirus type 1 but not for types 2 and 3, Two OPV doses fol lowing 3 IPV doses did not significantly increase seroprevalence or ra ise GMTs for poliovirus types 2 and 3; however, significant increases were found for poliovirus type 1, which may have benefitted from monov alent type I administration.