Oral polio vaccination and low case fatality at the paediatric ward in Bissau, Guinea-Bissau

Oral polio vaccine (OPV) and diphtheria-tetanus-pertussis (DTP) vaccines are given simultaneously in routine immunisation programmes in developing countries. It is therefore difficult to determine the separate effects of these vaccines on survival. We used the shortage of DTP vaccine in Bissau to examine the impact of OPV on the case fatality at the paediatric ward in Bissau. For 719 children less than 5 years of age whose vaccination card had been seen at admission and who had not yet received measles vaccine, having received OPV only was associated with a case fatality of 6% compared with 15% for children having received combined DTP and OPV vaccinations, the case fatality ratio (CFR) being 0.29 (95% confidence interval (CI) 0.11-0.77). Even if children fleeing the hospital were assumed to have died shortly after leaving the hospital, the case fatality would still be lower for children having received OPV only (CFR = 0.41; (95% CI 0.20-0.81)). The tendency was similar for children hospitalised with pneumonia, diarrhoea, and presumptive malaria. Control for background factors had no impact on the estimate. In areas with high mortality, OPV administered alone may have non-specific beneficial effects or DTP may have a negative effect for children who had received both DTP and OPV.