TY - JOUR
T1 - Herd protection by a bivalent killed whole-cell oral cholera vaccine in the slums of Kolkata, India
AU - Ali, Mohammad
AU - Sur, Dipika
AU - You, Young Ae
AU - Kanungo, Suman
AU - Sah, Binod
AU - Manna, Byomkesh
AU - Puri, Mahesh
AU - Wierzba, Thomas F.
AU - Donner, Allan
AU - Nair, G. Balakrish
AU - Bhattacharya, Sujit K.
AU - Dhingra, Mandeep Singh
AU - Deen, Jacqueline L.
AU - Lopez, Anna Lena
AU - Clemens, John
N1 - Funding Information:
Financial support. This work was supported by the Bill & Melinda Gates Foundation through the Diseases of the Most Impoverished Program and the Cholera Vaccine Initiative. Additional funding is provided by the Swedish International Development Cooperation Agency and the governments of South Korea, Sweden, and Kuwait. Shantha Biotechnics donated vaccine and placebo for the study. No funding bodies had any role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Potential conflicts of interest. All authors: No reported conflicts.
PY - 2013/4/15
Y1 - 2013/4/15
N2 - Background. We evaluated the herd protection conferred by an oral cholera vaccine using 2 approaches: cluster design and geographic information system (GIS) design.Methods. Residents living in 3933 dwellings (clusters) in Kolkata, India, were cluster-randomized to receive either cholera vaccine or oral placebo. Nonpregnant residents aged ≥1 year were invited to participate in the trial. Only the first episode of cholera detected for a subject between 14 and 1095 days after a second dose was considered. In the cluster design, indirect protection was assessed by comparing the incidence of cholera among nonparticipants in vaccine clusters vs those in placebo clusters. In the GIS analysis, herd protection was assessed by evaluating association between vaccine coverage among the population residing within 250 m of the household and the occurrence of cholera in that population.Results. Among 107 347 eligible residents, 66 990 received 2 doses of either cholera vaccine or placebo. In the cluster design, the 3-year data showed significant total protection (66% protection, 95% confidence interval [CI], 50%-78%, P <. 01) but no evidence of indirect protection. With the GIS approach, the risk of cholera among placebo recipients was inversely related to neighborhood-level vaccine coverage, and the trend was highly significant (P <. 01). This relationship held in multivariable models that also controlled for potentially confounding demographic variables (hazard ratio, 0.94 [95% CI,. 90-.98]; P <. 01).Conclusions. Indirect protection was evident in analyses using the GIS approach but not the cluster design approach, likely owing to considerable transmission of cholera between clusters, which would vitiate herd protection in the cluster analyses.
AB - Background. We evaluated the herd protection conferred by an oral cholera vaccine using 2 approaches: cluster design and geographic information system (GIS) design.Methods. Residents living in 3933 dwellings (clusters) in Kolkata, India, were cluster-randomized to receive either cholera vaccine or oral placebo. Nonpregnant residents aged ≥1 year were invited to participate in the trial. Only the first episode of cholera detected for a subject between 14 and 1095 days after a second dose was considered. In the cluster design, indirect protection was assessed by comparing the incidence of cholera among nonparticipants in vaccine clusters vs those in placebo clusters. In the GIS analysis, herd protection was assessed by evaluating association between vaccine coverage among the population residing within 250 m of the household and the occurrence of cholera in that population.Results. Among 107 347 eligible residents, 66 990 received 2 doses of either cholera vaccine or placebo. In the cluster design, the 3-year data showed significant total protection (66% protection, 95% confidence interval [CI], 50%-78%, P <. 01) but no evidence of indirect protection. With the GIS approach, the risk of cholera among placebo recipients was inversely related to neighborhood-level vaccine coverage, and the trend was highly significant (P <. 01). This relationship held in multivariable models that also controlled for potentially confounding demographic variables (hazard ratio, 0.94 [95% CI,. 90-.98]; P <. 01).Conclusions. Indirect protection was evident in analyses using the GIS approach but not the cluster design approach, likely owing to considerable transmission of cholera between clusters, which would vitiate herd protection in the cluster analyses.
KW - bivalent killed oral cholera vaccine
KW - cholera
KW - cluster randomized trial
KW - herd effect
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U2 - 10.1093/cid/cit009
DO - 10.1093/cid/cit009
M3 - Article
C2 - 23362293
AN - SCOPUS:84875640885
SN - 1058-4838
VL - 56
SP - 1123
EP - 1131
JO - Clinical Infectious Diseases
JF - Clinical Infectious Diseases
IS - 8
ER -