Household and Individual Risk Factors for Cholera among Cholera Vaccine Recipients in Rural Haiti.

Cholera remains a significant cause of morbidity and mortality worldwide, mainly affecting regions that do not have the population-level water, sanitation, and hygiene (WASH) infrastructure that eliminated the disease in Europe and North America over a century ago.1 Oral cholera vaccines (OCVs) are increasingly being deployed as part of a comprehensive approach to prevent cholera globally, and multiple studies have demonstrated their effectiveness.2 However, they do not provide complete protection; vaccinated individuals can still contract the disease.3–5 As such, understanding risk factors for cholera among populations that have been vaccinated against cholera is of critical importance to determine how to design comprehensive integrated programs to eliminate transmission of cholera in the near term. Risk factors for infectious diseases such as cholera vary in space and time, depending on the social, environmental, and biological contexts in which they occur.6,7 Cholera outbreaks have been attributed to population-level risk factors including climate conditions,8 the presence of specific copepod hosts,8 and human migration patterns, among others.9 Individual-level risk factors for cholera have also been well-described and include inadequate WASH,10 ingestion of contaminated food or beverages,11 and host characteristics (i.e., blood group O, retinol deficiency).12,13 Previous studies have demonstrated how population-level immunity can modulate other risk factors for cholera, such as the risk associated with weather fluctuations,14 and how cholera vaccination campaigns can improve knowledge and practices related to diarrheal disease15; these suggest that vaccination may modulate biological, behavioral, and environmental susceptibility to cholera. However, to our knowledge, no study has examined the specific factors that contribute to cholera disease among vaccinated individuals. Currently, there are three available OCVs prequalified by the World Health Organization (WHO): Dukoral® (SBLVAccin, Stockholm, Sweden), Shanchol® (Shantha Biotechnics, Hyderabad, India) and Euvichol® (Eubiologics, Seoul, South Korea).2,16 A stockpile containing millions of doses of OCV for deployment and distribution to cholera epidemic and endemic areas, including Haiti, was created in 2013 by the WHO.17 As the use of OCV continues to expand globally, an understanding of modifiable risk factors among vaccine recipients will inform which nonimmunologic interventions, in particular WASH approaches, might best be used to complement OCV vaccination campaigns in the immediate and near term, when epidemics are underway. In this context, we present the first assessment of risk factors for cholera among OCV recipients, identified through secondary analyses of a field-based case-control study to evaluate OCV effectiveness in rural Haiti.3