Trial of a supplemental dose of four poliovirus vaccines

Background: The immunogenicity of oral poliovirus vaccine (OPV), particular ly the type 3 component, is lower in infants in most developing countries t han in infants in industrialized countries. We conducted a multicenter tria l in Oman to evaluate the response to a supplemental dose of four polioviru s vaccine formulations. Methods: At nine months of age, infants were randomly assigned to receive i nactivated-poliovirus vaccine (IPV), administered subcutaneously; trivalent OPV manufactured in the United States or in Europe; or monovalent type 3 O PV. Serum samples were collected at enrollment and 7 and 30 days later. All of the infants had previously received five doses of OPV. Results: We enrolled 1025 infants; 785 (76.6 percent) met all the study req uirements. At enrollment, 96.8 percent of the infants were seropositive for poliovirus type 1, 98.0 percent for type 2, and 88.0 percent for type 3. A t 30 days there were no significant increases in type 3 seroprevalence or i n the median antibody titer in the groups of infants who received OPV. Amon g the recipients of IPV, type 3 seroprevalence increased from 87.8 percent at enrollment to 97.1 percent at 30 days (P<0.001), and the median antibody titer increased from 1:228 to 1:1448 or higher (P<0.001). The rapid initia l increase in the antibody titer suggests a secondary immune response. Conclusions: A supplemental dose of IPV has excellent immunogenicity and le ads to increases in the titer of antibodies against type 3 poliovirus, wher eas supplemental doses of the oral vaccines do not have these effects. (N E ngl J Med 2000;343:767-73.) (C) 2000, Massachusetts Medical Society.