Abstract
BackgroundCholera is known to be transmitted from person to person, and inactivated oral cholera vaccines (OCVs) have been shown to confer herd protection via interruption of this transmission. However, the geographic dimensions of chains of person-to-person transmission of cholera are uncertain. The ability of OCVs to confer herd protection was used to define these dimensions in two cholera-endemic settings, one in rural Bangladesh and the other in urban India. MethodsTwo large randomized, placebo-controlled trials of inactivated OCVs, one in rural Matlab, Bangladesh and the other in urban Kolkata, India, were reanalyzed. Vaccine herd protection was evaluated by relating the risk of cholera in placebo recipients to vaccine coverage of surrounding residents residing within concentric rings. In Matlab, concentric rings in 100-m increments up to 700m were evaluated; in Kolkata, 50-m increments up to 350m were evaluated. ResultsOne hundred and eight cholera cases among 24667 placebo recipients were detected during 1year of post-vaccination follow-up at Matlab; 128 cholera cases among 34968 placebo recipients were detected during 3 years of follow-up in Kolkata. Consistent inverse relationships were observed between vaccine coverage of the ring and the risk of cholera in the central placebo recipient for rings with radii up to 500m in Matlab and up to 150m in Kolkata. ConclusionsThese results suggest that the dimensions of chains of person-to-person transmission in endemic settings can be quite large and may differ substantially from setting to setting. Using OCVs as ‘probes’ to define these dimensions can inform geographical targeting strategies for the deployment of these vaccines in endemic settings.
Highlights
Killed oral cholera vaccines (OCVs) are stockpiled by the World Health Organization (WHO) and are recommended public health tools for the control of cholera outbreaks (Martin et al, 2012)
Knowledge of the geographic dimensions of chains of person-to-person cholera transmission will be important for effective geographic targeting, as OCVs have been demonstrated to confer both direct protection to vaccinees and herd protection to populations, the latter operating via interruption of person-to-person transmission
108 cholera cases occurred among 24 667 recipients of at least two doses of placebo during the 1 year of follow-up in Matlab; 128 cholera cases occurred among 34 968 two-dose placebo recipients during the 3 years of follow-up in Kolkata
Summary
Killed oral cholera vaccines (OCVs) are stockpiled by the World Health Organization (WHO) and are recommended public health tools for the control of cholera outbreaks (Martin et al, 2012). M. Ali et al / International Journal of Infectious Diseases 66 (2018) 90–95 person cholera transmission, delineation of the dimensions of OCV herd protection should demarcate the dimensions of chains of person-to-person transmission. Cholera is known to be transmitted from person to person, and inactivated oral cholera vaccines (OCVs) have been shown to confer herd protection via interruption of this transmission. The ability of OCVs to confer herd protection was used to define these dimensions in two cholera-endemic settings, one in rural Bangladesh and the other in urban India. Methods: Two large randomized, placebo-controlled trials of inactivated OCVs, one in rural Matlab, Bangladesh and the other in urban Kolkata, India, were reanalyzed. Vaccine herd protection was evaluated by relating the risk of cholera in placebo recipients to vaccine coverage of surrounding residents residing within concentric rings.
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