|WHO recommends oral polio vaccine at birth (OPV0) in low income countries. OPV is furthermore provided at 6, 10, and 14 weeks of age (OPV1-3). However, observational data from the Bandim Health Project (BHP) suggested that OPV0 could have unexpected negative effects for boys; as boys who did not receive OPV0 due to a temporary lack of OPV in Guinea-Bissau in 2004 had lower mortality than boys who got OPV0.
This PhD dissertation consists of four papers exploring the effects of OPV0 on mortality, growth, morbidity, and polio antibody titres. We studied normal birth weight (NBW) children in the BHP study area and low birth weight (LBW) children from the whole capital.
Paper I is based on observational data from a randomised controlled trial conducted from 2004-2007. While conducting a trial of BCG and vitamin A supplementation (VAS) at birth to LBW children, OPV was lacking for a short period. We compared the 99 children who missed OPV0 with the 243 children enrolled from 2 months before to 2 months after the period with missing OPV and with all 2198 children who received OPV0 during the trial. Missing OPV0 was associated with a tendency towards higher mortality during the first year of life, the adjusted Hazard ratio (aHR) being 1.63 (95 % CI: 0.83 - 3.19) in both boys and girls.
Paper II reports results from a randomised, controlled, open trial investigating whether VAS at birth instead of OPV0 could lower infant mortality for LBW boys. Newborn boys were randomised to OPV0 or VAS and no OPV0 and followed for 12 months. In the rainy season we detected a cluster of deaths in the VAS group and the trial was halted immediately. The VAS group had significantly higher mortality than the OPV0 group in the rainy season (HR: 9.91 (1.23-80)). All deaths had had contact with the neonatal nursery; of seven VAS boys enrolled in September, six died within two months, whereas only one died among the six OPV0 boys (p for interaction=0.05). It was not possible to identify any specific pathogen which might have been the cause of the cluster of deaths. Growth (weight, length, arm-circumference) in the OPV0 group was significantly better until age 3 months.
Papers III and IV describe results from an open trial randomising 7000 NBW newborns to OPV0 and BCG as recommended or BCG alone. Paper III describes growth of a subgroup of 1259 children and morbidity in a subgroup of 820 children. Length, weight, head and arm circumference were measured in the anthropometry subgroup at 6 weeks, 6 months, and 12 months of age. We found no differences in any of these parameters between the two groups. Nor were there any overall differences between the two groups when examined for morbidity in the month after enrolment.
Paper IV evaluates the effect of OPV0 on antibody titres against polio virus in blood samples from a subgroup of 378 children. Not receiving OPV0 was associated with significantly lower antibody titres at 6 weeks of age (Geometric Mean Ratio 0.53 (0.34-0.80)). In contrast, at 6 months of age children who had not received OPV0 had significantly higher titres of polio 1 neutralising antibodies (1.43 (1.05-1.96)). These effects were only significant for boys.
In conclusion, our studies do not support that OPV0 has negative effects for boys; in contrast the studies suggest that OPV0 provides some non-specific benefits for both sexes. We are awaiting the mortality results of the large randomised trial. If the results support that OPV0 has beneficial effect this should be taken into consideration in the long term plans of replacing OPV with inactivated polio vaccine in the approaches towards polio eradication.