Oral polio vaccination and low case fatality at the paediatric ward in Bissau, Guinea-Bissau
Introduction
In areas with high child mortality, routine immunisations may have important non-specific effects on survival [1], [2], [3], [4], [5], [6]. For example, high-titre measles vaccine was protective against measles infection but associated with increased mortality when compared with standard measles vaccine [3]. Effects have been markedly positive when BCG, often given with oral polio vaccine (OPV), or measles vaccine was the last vaccine received [1], [2], [4]. However, in several studies from West Africa, diphtheria–tetanus–pertussis (DTP) and OPV vaccines have not been associated with reduced mortality [1], [2], [4], [5], [6]. Since DTP and OPV vaccines are usually administered together, it is difficult to distinguish the separate effects of these vaccines. Recently, the provision of DTP has been irregular in Guinea-Bissau. We therefore used the occasional shortage of DTP in Bissau city to assess the separate impact of OPV on the case fatality at the paediatric ward.
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Subjects and methods
From May 2001 to April 2002, we registered all children hospitalised at the only paediatric ward in Bissau to examine the possible impact of immunisation status on the in-hospital case fatality. The recommended vaccination schedule in Bissau is BCG and OPV at birth and simultaneous doses of DTP and OPV at 6, 10, and 14 weeks of age, and finally measles vaccine at 9 months of age. During the present study, DTP was missing from the local health centres during May–June and August–September 2001,
Results
Among the 2126 children who had their vaccination card inspected, 719 had received either OPV only or DTP and OPV and no measles vaccine yet, the case fatality being 14% (102/719). Controlling for age, children who had received OPV only had a CFR of 0.29 (95% CI 0.11–0.77) compared with the children who had received both DTP1 and OPV (Table 1). Controlling for both age and number of vaccination doses, children who had received OPV only had a CFR of 0.29 (95% CI 0.11–0.77) compared with the
Discussion
When oral polio was introduced in the 1960s, a Chilean study observed a significant reduction in mortality and suggested that the effect could be due to OPV virus limiting the replication of other enterovirus [7]. In randomised studies conducted in the Soviet Union in the 1950s and 1960s, Voroshilova found a marked reduction in gastrointestinal and respiratory morbidity associated with the use of non-pathogenic enterovirus vaccines including OPV [8]. Following national polio immunisation days
Acknowledgements
Contributors: A.R. and P.A. planned the study in collaboration with S.B., C.M. and J.E.V. who established the hospital register. A.R., H.J., C.B. and P.A. planned the analyses. P.A. wrote the first version of the paper, and all authors contributed to the final version. Conflict of interest statement: None declared. Funding: Research was funded from The Council for Development Research, Denmark, and the EU Commission (IC18CT95-0011). P.A. holds a research professorship funded by the Novo Nordisk
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