Spatial and environmental connectivity analysis in a cholera vaccine trial.
This paper develops theory and methods for vaccine trials that utilize spatial and environmental information. Satellite imagery is used to identify whether households are connected to one another via water bodies in a study area in rural Bangladesh. Then relationships between neighborhood-level cholera vaccine coverage and placebo incidence and neighborhood-level spatial variables are measured. The study hypothesis is that unvaccinated people who are environmentally connected to people who have been vaccinated will be at lower risk compared to unvaccinated people who are environmentally connected to people who have not been vaccinated. We use four datasets including: a cholera vaccine trial database, a longitudinal demographic database of the rural population from which the vaccine trial participants were selected, a household-level geographic information system (GIS) database of the same study area, and high resolution Quickbird satellite imagery. An environmental connectivity metric was constructed by integrating the satellite imagery with the vaccine and demographic databases linked with GIS. The results show that there is a relationship between neighborhood rates of cholera vaccination and placebo incidence. Thus, people are indirectly protected when more people in their environmentally connected neighborhood are vaccinated. This result is similar to our previous work that used a simpler Euclidean distance neighborhood to measure neighborhood vaccine coverage [Ali, M., Emch, M., von Seidlein, L., Yunus, M., Sack, D. A., Holmgren, J., et al. (2005). Herd immunity conferred by killed oral cholera vaccines in Bangladesh. Lancet, 366(9479), 44-49]. Our new method of measuring environmental connectivity is more precise since it takes into account the transmission mode of cholera and therefore this study validates our assertion that the oral cholera vaccine provides indirect protection in addition to direct protection.
Emch
Michael
M
Department of Geography, University of North Carolina, Saunders Hall, Campus Box 3220, Chapel Hill, NC 27599-3220, USA. emch@mail.unc.edu
Ali
Mohammad
M
Root
Elisabeth D
ED
Yunus
Mohammad
M
D000293:Adolescent; D000328:Adult; D001459:Bangladesh; D002648:Child; D002675:Child, Preschool; D022121:Cholera Vaccines / Q000008:administration & dosage / Q000276:immunology*; D017326:Clinical Trials, Phase III as Topic; D005260:Female; D040362:Geographic Information Systems; D006801:Humans; D032521:Immunity, Herd; D008297:Male; D008954:Models, Biological; D016017:Odds Ratio; D010919:Placebos; D012111:Residence Characteristics; D045483:Rivers; D012424:Rural Population; D055815:Young Adult
D022121:Cholera Vaccines; D010919:Placebos