Childhood mortality after oral polio immunisation campaign in Guinea-Bissau
Introduction
When oral polio was introduced in the 1960s, a Chilean study observed a significant reduction in mortality and suggested that Sabin's oral polio vaccine virus limited other enteroviruses [1]. In studies conducted in the Soviet Union in the 1950s and 1960s, Voroshilova found marked reduction in morbidity associated with the use of non-pathogenic enterovirus vaccines including oral polio vaccine (OPV) [2]. If such effects were indeed true, it would add to the value of national polio immunisation days but would also question the health impact of dropping oral polio vaccination in the later stages of polio eradication [3]. Surprisingly, the effect of national polio immunization days on morbidity and mortality has not been examined previously.
The major reason for undertaking the present study was the observation that routine immunisations may have important non-specific effects for childhood survival [4], [5], [6], [7], [8]. BCG and measles vaccine have been associated with marked reduction in mortality, which cannot be explained by the prevention of measles or tuberculosis [4], [5]. However, diphtheria, tetanus, pertussis (DTP) and OPV have been associated with no reduction or slightly increased mortality [4], [5], [7], [8]. Since DTP and polio vaccines are usually administered together at 6, 10, and 14 weeks of age in the immunisation programme in low-income countries, it is difficult to distinguish the effects of these vaccines. We therefore used the opportunity of national polio immunisation days in 1998 in Guinea-Bissau to assess the effect on child survival of oral polio vaccine administered alone.
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Subjects and methods
The Bandim Health Project (BHP) has maintained a population register for the inhabitants of the districts of Bandim 1, Bandim 2, Belem, and Mindara in the capital of Guinea-Bissau since 1978, 1984, 1984, and 1995, respectively. All houses in the study area are visited monthly to identify pregnant women and newborn children. Field workers from the Bandim Health Project (BHP) visit all children at home every 3 months until the age of 3 years. Information is collected routinely on breastfeeding
Results
A total of 6159 children less than 5 years of age were registered in the area. When houses were visited in March 1998, 6103 were still living in the area. Information on polio vaccination could not be obtained for 19.0% (1162/6103) of the children, mainly because the family was travelling. Of the children less than 5 years of age, 17.7% (875/4941) had not received polio vaccine. Many had been travelling while the campaign was conducted. The vaccination coverage differed by source of
Discussion
Our data suggest that OPV administered alone during the campaign was not associated with any adverse morbidity or mortality and might even be associated with a lower risk of hospitalisation and mortality for the youngest children less than 6 months of age. As in several other studies [4], there was a marked beneficial effect of measles vaccine, mortality being 56% lower among measles-vaccinated children (Table 2). Given the strong effect of measles vaccine, the effects of other vaccines are
Acknowledgements
Contributors: The study was planned in 1998 by PA, AS, EN, IL, and HJ. JEV maintained the hospital register. HJ, MS and MJ were responsible for survival follow-up after the war. KH and HJ carried out the statistical analyses. PA wrote the first version of the paper and all authors contributed to the final version. Coflict of interest statement: None declared. Funding: Research was funded from ECHO, Bruxelles, the Council for Development Research, Denmark, and the EU Commission (IC18CT95-0011).
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