COMPARISON OF ENHANCED POTENCY INACTIVATED POLIOVIRUS VACCINE (EIPV) VERSUS STANDARD ORAL POLIOVIRUS VACCINE (OPV) IN THAI INFANTS

Enhanced potency inactivated poliovirus vaccine (EIPV), combined with diphteria-tetanus-pertussis (DTP) vaccine, was compared with oral poli ovirus vaccine (OPV) regarding immunogenicity in Thai infants, vaccina ted at 2, 4 and 6 months of age, EIPV induced significantly higher ser oconversion rates than OPV to ail 3 poliovirus types after the second and third immunization, After 3 doses of each vaccine, at 7 months of age, all infants receiving EIPV proved seropositive for poliovirus typ e I, type 2 and type 3 neutralizing antibodies, whereas of those recei ving OPV, 9% remained seronegative (titre <1:4) for type 1 (p=0.0042) and 11% for type 3 (p = 0.0013). All participating children were given an additional dose of OPV at the age of 9 months and tested again at 12 months of age. At that point, virtually all infants had poliovirus neutralizing antibodies, but the geometric mean titres to each poliovi rus type were significantly higher in the vaccinees who had received E IPV. It is concluded that the greater immunogenicity of EIPV vis-a-vis 3 doses of OPV may be biologically significant for protection against poliovirus types 1 and 3 in countries where cases of poliomyelitis oc cur in young children. These Endings warrant considering EIPV, alone o r in combination with OPV, for an immunization programme in Thailand a nd similar countries in the future.