HOST AND VIRAL FACTORS AFFECTING THE DECREASED IMMUNOGENICITY OF SABIN TYPE-3 VACCINE AFTER ADMINISTRATION OF TRIVALENT ORAL POLIO VACCINE TO RURAL MAYAN CHILDREN

Factors affecting immunogenicity of the first 2 doses of oral poliovir us vaccine (OPV) among unimmunized Mayan infants were prospectively ev aluated. The relative impact of multiple variables, including mass or routine vaccination, concurrent enteric bacterial (salmonella, shigell a, and campylobacter) and viral (adenovirus 40/41, astrovirus, nonpoli o enteroviruses, and rotavirus) infections, interference among Sabin v accine viruses, and preexisting poliovirus antibodies were studied. Se ra were available from 181 infants after 2 OPV doses. Seroresponses we re 86% to Sabin type 1, 97% to Sabin type 2, and 61% to Sabin type 3 v accines. Mass versus routine vaccination and preexisting poliovirus an tibodies did not affect immunogenicity. By multiple logistic regressio n analysis, fecal shedding of homologous Sabin strains was associated with increased seroresponses to all Sabin types, especially to Sabin t ype 3. Decreased OPV immunogenicity was primarily attributable to inte rference of Sabin type 3 by Sabin type 2. OPV formulations with higher doses of Sabin type 3 could improve immunogenicity among infants in d eveloping countries.