Cholera in Haiti – Authors' reply
Authors: Elizabeth C Lee, Ralph Ternier, Justin Lessler, Andrew S Azman, Louise C Ivers
Journal: The Lancet Global Health (2020)

We appreciate the careful consideration of our Article1Lee EC Chao DL Lemaitre JC et al.Achieving coordinated national immunity and cholera elimination in Haiti through vaccination: a modelling study.Lancet Glob Health. 2020; 8: e1081-e1089Summary Full Text Full Text PDF PubMed Scopus (5) Google Scholar from Stanislas Rebaudet and colleagues and Jean Hugues Henrys and colleagues, but we must respectfully disagree with most of their concerns about our study. Our work sought to understand the potential impact of mass oral cholera vaccination campaigns and their consequent synchronisation of population immunity in the unique Haitian context, where local transmission in the Americas was geographically isolated and importation risk has been historically low. This modelling study in no way constitutes a recommendation for a national cholera vaccination campaign in Haiti. The Bill & Melinda Gates Foundation and other funding organisations during the conduct and outside of our study had no role in the concept, design, data collection, writing, review of, or decision to publish these results. Our work explores the potential impact of the campaigns that had been planned by the Haitian Ministry of Health at the start of the study, and of campaigns with a larger scope.2Ministère de la Santé Publique et de la Population et Direction Nationale de L'Eau Potable et de L'Assainissement République d'HaïtiPlan national d'élimination du choléra, développement du moyen terme, Juillet 2016–Décembre 2018. Ministère de la Santé Publique et de la Population et Direction Nationale de L'Eau Potable et de L'Assainissement, République d'Haïti, 2016Google Scholar As more countries set their sights on cholera elimination, understanding situations where mass oral cholera vaccination campaigns could produce long-lasting effects is crucial because supplies of vaccine are scarce. The study design, objectives, and our conclusions were informed by multiple collaborative consultations with colleagues in the public health sector in Haiti. Recognising that individual models might provide unreliable predictions, we focused on consensus results across models with different assumptions about cholera transmission, interventions, and immunity in the Haitian population. Although we did not individually model water and sanitation improvements and other non-vaccination interventions, this approach does not invalidate our results. Our work assessed the effect of vaccine on top of existing measures, because the model calibration procedures estimated transmission parameters under the empirically observed conditions (not in the absence of all interventions) from Oct 23, 2010, to January, 2019, the time of analysis. Furthermore, because most models were simulated at the department scale, these relatively macro-level disease dynamics would probably prevail over the effect of small-scale interventions with unclear effectiveness. We modelled underlying infections and applied a theoretical definition of elimination: less than one infection of Vibrio cholerae over a consecutive 1-year period. We recognise that it would be near-impossible for a surveillance system to certify zero infections in a real-world setting, but a simulation study does not need a proxy definition of elimination; elimination can be determined directly. Rebaudet and colleagues expressed concern about the early median times to elimination in the no-vaccination scenario, but this might stem from their misinterpretation of the results. Almost all model-scenario combinations predicted a small probability of elimination shortly after the end of the calibration period (meaning that the absence of cases after February, 2019, was within the predicted range of outcomes). However, an increased proportion of simulations that would have had persistent transmission actually achieved elimination under vaccination scenarios in our study; thus, median times to elimination were delayed relative to the no-vaccination scenario because additional simulated eliminations were caused by the vaccination campaign. Rebaudet and colleagues are nevertheless justified in their concern that few simulations projected the absence of confirmed cases since February, 2019, and we acknowledged this fact in our Article and discussed potential contributing factors. However, we stand by the fact that the absence of reported cases could be due to limitations in surveillance. We do not dispute that the total number of cases of diarrhoea in Haiti has been substantially reduced and cholera is well controlled in Haiti, but the absence of reported cases does not necessarily mean that cholera is completely absent. The Haitian National Surveillance System has performed very well under extremely challenging circumstances, and we applaud the work of the Ministry of Health and partners. But when elimination (not just disease control) is the objective, a surveillance system must be even more exacting to reach even a pragmatic, public health definition of elimination. Although the global cholera community has not defined the minimum requirements of a surveillance system to declare elimination, these requirements might reasonably include active case finding, enhanced laboratory surveillance of a representative sample of individuals with diarrhoea and all individuals with suspected cholera, and community-based surveillance. Through consultations with implementers and Haitian public health officials and, because several study coauthors work in the rural health system of Haiti, we are aware of some gaps between the laudable stated goals of cholera surveillance and actual delivery. For example, interruptions in ability to transport samples during extended periods of sociopolitical crisis in 2019, minimal decentralised laboratory infrastructure for stool sample cultures, and from April to August, 2020, large reductions in attendance for diarrhoea at health centres in the Centre and Artibonite departments of Haiti while the health system responded to COVID-19. In epidemiologic weeks 1–33 of 2020, one decentralised laboratory did only 183 stool sample cultures for a geographical region with a population of 3·8 million people.3Register of laboratory specimens, St Marc, Haiti. In a report shared with partners by Laboratoire National de Santé Publique, Sept 9, 2020.Google Scholar Coupled with high rates of self-administration of antibiotics in general outpatient visits,4Moise K Bernard JJ Henrys JH Evaluation of antibiotic self-medication among outpatients of the state university hospital of Port-Au-Prince, Haiti: a cross-sectional study.Pan Afr Med J. 2017; 28: 4Crossref PubMed Scopus (8) Google Scholar and imperfect sensitivity of culture for V cholerae,5Alam M Hasan NA Sultana M et al.Diagnostic limitations to accurate diagnosis of cholera.J Clin Microbiol. 2010; 48: 3918-3922Crossref PubMed Scopus (54) Google Scholar V cholerae O1 infections could reasonably be missed. We are aligned with Henrys and colleagues and Rebaudet and colleagues in our desire to ensure sustained control of cholera in Haiti, and believe elimination is possible. Reinforcing surveillance, and in some places executing on already-planned enhancements, will be an important way to document that goal. The declaration of interests remain the same as in the original Article. Achieving coordinated national immunity and cholera elimination in Haiti through vaccination: a modelling studyModels suggest that the probability of achieving zero transmission of Vibrio cholerae in Haiti with current methods of control is low, and that bolder action is needed to promote elimination of cholera from the region. Large-scale cholera vaccination campaigns in Haiti would offer the opportunity to synchronise nationwide immunity, providing near-term population protection while improvements to water and sanitation promote long-term cholera elimination. Full-Text PDF Open AccessCholera in HaitiWe were very surprised to read the recently published Article by Elizabeth Lee and colleagues1 and the linked Comment by Jeannot François.2 We believe both pieces might deeply mislead readers about the current epidemiological situation of cholera in Haiti. Full-Text PDF Open AccessCholera in HaitiWe carefully read the recently published study by Elizabeth Lee and colleagues (August, 2020).1 We have substantial concerns about the results of the four models, which are in contrast with the current absence of actual cholera cases in Haiti since February, 2019. Full-Text PDF Open Access