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      Protection against cholera from killed whole-cell oral cholera vaccines: a systematic review and meta-analysis

      research-article
      , MHS a , , MPH b , c , , PhD d , , MD d , , MD e , f , , MD g , , PhD h , , MD i , , Prof, MD j , , PhD j , , PhD a , , PhD j , k , , Dr, PhD a , l , * , Oral Cholera Vaccine Working Group of The Global Task Force on Cholera Control
      The Lancet. Infectious Diseases
      Elsevier Science ;, The Lancet Pub. Group

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          Summary

          Background

          Killed whole-cell oral cholera vaccines (kOCVs) are becoming a standard cholera control and prevention tool. However, vaccine efficacy and direct effectiveness estimates have varied, with differences in study design, location, follow-up duration, and vaccine composition posing challenges for public health decision making. We did a systematic review and meta-analysis to generate average estimates of kOCV efficacy and direct effectiveness from the available literature.

          Methods

          For this systematic review and meta-analysis, we searched PubMed, Embase, Scopus, and the Cochrane Review Library on July 9, 2016, and ISI Web of Science on July 11, 2016, for randomised controlled trials and observational studies that reported estimates of direct protection against medically attended confirmed cholera conferred by kOCVs. We included studies published on any date in English, Spanish, French, or Chinese. We extracted from the published reports the primary efficacy and effectiveness estimates from each study and also estimates according to number of vaccine doses, duration, and age group. The main study outcome was average efficacy and direct effectiveness of two kOCV doses, which we estimated with random-effect models. This study is registered with PROSPERO, number CRD42016048232.

          Findings

          Seven trials (with 695 patients with cholera) and six observational studies (217 patients with cholera) met the inclusion criteria, with an average two-dose efficacy of 58% (95% CI 42–69, I 2=58%) and effectiveness of 76% (62–85, I 2=0). Average two-dose efficacy in children younger than 5 years (30% [95% CI 15–42], I 2=0%) was lower than in those 5 years or older (64% [58–70], I 2=0%; p<0·0001). Two-dose efficacy estimates of kOCV were similar during the first 2 years after vaccination, with estimates of 56% (95% CI 42–66, I 2=45%) in the first year and 59% (49–67, I 2=0) in the second year. The efficacy reduced to 39% (13 to 57, I 2=48%) in the third year, and 26% (−46 to 63, I 2=74%) in the fourth year.

          Interpretation

          Two kOCV doses provide protection against cholera for at least 3 years. One kOCV dose provides at least short-term protection, which has important implications for outbreak management. kOCVs are effective tools for cholera control.

          Funding

          The Bill & Melinda Gates Foundation.

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          Most cited references39

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          Updated Global Burden of Cholera in Endemic Countries

          Background The global burden of cholera is largely unknown because the majority of cases are not reported. The low reporting can be attributed to limited capacity of epidemiological surveillance and laboratories, as well as social, political, and economic disincentives for reporting. We previously estimated 2.8 million cases and 91,000 deaths annually due to cholera in 51 endemic countries. A major limitation in our previous estimate was that the endemic and non-endemic countries were defined based on the countries’ reported cholera cases. We overcame the limitation with the use of a spatial modelling technique in defining endemic countries, and accordingly updated the estimates of the global burden of cholera. Methods/Principal Findings Countries were classified as cholera endemic, cholera non-endemic, or cholera-free based on whether a spatial regression model predicted an incidence rate over a certain threshold in at least three of five years (2008-2012). The at-risk populations were calculated for each country based on the percent of the country without sustainable access to improved sanitation facilities. Incidence rates from population-based published studies were used to calculate the estimated annual number of cases in endemic countries. The number of annual cholera deaths was calculated using inverse variance-weighted average case-fatality rate (CFRs) from literature-based CFR estimates. We found that approximately 1.3 billion people are at risk for cholera in endemic countries. An estimated 2.86 million cholera cases (uncertainty range: 1.3m-4.0m) occur annually in endemic countries. Among these cases, there are an estimated 95,000 deaths (uncertainty range: 21,000-143,000). Conclusion/Significance The global burden of cholera remains high. Sub-Saharan Africa accounts for the majority of this burden. Our findings can inform programmatic decision-making for cholera control.
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            A comparison of heterogeneity variance estimators in combining results of studies.

            For random effects meta-analysis, seven different estimators of the heterogeneity variance are compared and assessed using a simulation study. The seven estimators are the variance component type estimator (VC), the method of moments estimator (MM), the maximum likelihood estimator (ML), the restricted maximum likelihood estimator (REML), the empirical Bayes estimator (EB), the model error variance type estimator (MV), and a variation of the MV estimator (MVvc). The performance of the estimators is compared in terms of both bias and mean squared error, using Monte Carlo simulation. The results show that the REML and especially the ML and MM estimators are not accurate, having large biases unless the true heterogeneity variance is small. The VC estimator tends to overestimate the heterogeneity variance in general, but is quite accurate when the number of studies is large. The MV estimator is not a good estimator when the heterogeneity variance is small to moderate, but it is reasonably accurate when the heterogeneity variance is large. The MVvc estimator is an improved estimator compared to the MV estimator, especially for small to moderate values of the heterogeneity variance. The two estimators MVvc and EB are found to be the most accurate in general, particularly when the heterogeneity variance is moderate to large.
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              Matrix product ansatz for Fermi fields in one dimension

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                Author and article information

                Contributors
                Journal
                Lancet Infect Dis
                Lancet Infect Dis
                The Lancet. Infectious Diseases
                Elsevier Science ;, The Lancet Pub. Group
                1473-3099
                1474-4457
                1 October 2017
                October 2017
                : 17
                : 10
                : 1080-1088
                Affiliations
                [a ]Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
                [b ]Environmental and Cancer Epidemiology Unit, National Centre for Epidemiology, Carlos III Institute of Health, Madrid, Spain
                [c ]Consortium for Biomedical Research in Epidemiology and Public Health (CIBERESP), Carlos III Institute of Health, Madrid, Spain
                [d ]World Health Organization, Geneva, Switzerland
                [e ]Department of Medicine, Division of Global Health Equity, Brigham and Women's Hospital, Boston, MA, USA
                [f ]Department of Global Health and Social Medicine, Harvard Medical School, Boston, MA, USA
                [g ]United States Centers for Disease Control and Prevention, Atlanta, GA, USA
                [h ]International Centre for Diarrhoeal Disease Research Bangladesh, Dhaka, Bangladesh
                [i ]International Vaccine Institute, Seoul, South Korea
                [j ]Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
                [k ]Epicentre, Paris, France
                [l ]Médecins Sans Frontières, Geneva, Switzerland
                Author notes
                [* ]Correspondence to: Dr Andrew S Azman, Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USACorrespondence to: Dr Andrew S AzmanDepartment of EpidemiologyJohns Hopkins Bloomberg School of Public HealthBaltimoreMD21205USA azman@ 123456jhu.edu
                [†]

                Members listed in the appendix

                Article
                S1473-3099(17)30359-6
                10.1016/S1473-3099(17)30359-6
                5639147
                28729167
                c0dddf1a-438a-453e-aea1-9a96d748dc12
                © 2017 World Health Organization

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/).

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                Categories
                Article

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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