Serological evaluation of a simplified immunization schedule using quadruple DPT-polio vaccine in Burkina Faso.

The immunogenicity of quadruple DPT-polio vaccine used in a two-dose regimen was investigated in a cross-sectional serological survey involving 355 children under 5 years of age. This schedule is currently applied in the EPI programme in three provinces in Burkina Faso, West Africa. It was found that two doses of quadruple DPT-polio vaccine induced antibodies at protective levels to diphtheria and tetanus toxin, and to the three types of polioviruses in over 90% of 179 children. The persistence of antibodies to tetanus and polioviruses is good, since over 90% of the children studied still had antibodies more than 2 years after their last vaccination. The antibodies to diphtheria toxin tend to decline in the first 6 months after vaccination, which is not uncommon. However, our data indicate clearly that a very high percentage (98%) of children have been primed to diphtheria toxin. Of 176 non-vaccinated children, up to 25% of the older ones had antibodies to polioviruses, most of them only to one type. This appears to be a sensitive parameter for the circulation of wild polioviruses in the environment. As the vaccination coverage in the study area was low (< 60%), it was to be expected that the circulation of polioviruses in the community could not be interrupted. The present study demonstrates the applicability of a two-dose strategy for primary immunization with a quadruple DPT-polio vaccine especially for poliovirus components and the toxoids. To induce pertussis immunity, however, a third vaccination is recommended.