Abstract
The population level effectiveness of a vaccine may arise as the result of direct protection of vaccinees and vaccine herd protection, which may protect non-vaccinees, vaccinees, or both. Indirect, total, enhanced, and overall vaccine protection are measures of vaccine herd protection. The level of population level effectiveness induced by a vaccine is driven by several factors, including known vaccine-induced protective efficacy, the magnitude, and distribution of vaccine coverage at a point in time and the extent to which different groups mix with one another in the community. Data on vaccine herd protection are valuable in understanding the importance and cost-effectiveness in deploying the e vaccine in public health program. Killed whole-cell (WC) oral cholera vaccines (OCVs) have been evaluated for herd protection in various study settings, leveraging geographic information system (GIS) tools for the analyses. This article provides a brief description of the herd protective effects of killed WC OCVs measured using various study deigns that include (a) individually randomized, controlled clinical trials, (b) cluster randomized clinical trials, (c) observational cohort studies, and (d) observational case-control studies. In all of the study designs, significant herd protection was observed in unvaccinated persons as well as in the community as a whole. The findings of these studies suggest that using killed WC OCV as a public health tool for controlling cholera is impactful and cost-effective.
Highlights
For pathogens transmitted from person to person, vaccination of a community may reduce pathogen transmission and thereby confer protection to the community beyond that expected on the basis of direct vaccine protection of vaccinees
By classifying the VIRTUAL CLUSTER LEVEL COVERAGE (VCLC) of killed WC oral cholera vaccines (OCVs) into quintiles of ascending vaccine coverage, we observed that the risk of cholera in persons who took at least two complete doses of placebo was inversely related to the VCLC of killed WC OCV as one moved from one level of coverage to the higher level; the same was true of the risk of cholera in vaccinees (Table 2) [3]
The study showed that the risk of cholera in young children was inversely related to the CLVC of killed WC OCV in older children and adult women, ranging from 18.9 cases per 1,000 children residing in areas with the lowest quintile of killed WC OCV coverage to 8.6 cases per 1,000 children in areas with the highest quintile of killed WC OCV coverage (Table 7)
Summary
Data on vaccine herd protection are valuable in understanding the importance and cost-effectiveness in deploying the e vaccine in public health program. Killed whole-cell (WC) oral cholera vaccines (OCVs) have been evaluated for herd protection in various study settings, leveraging geographic information system (GIS) tools for the analyses. In all of the study designs, significant herd protection was observed in unvaccinated persons as well as in the community as a whole. The findings of these studies suggest that using killed WC OCV as a public health tool for controlling cholera is impactful and cost-effective
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