TY - JOUR
T1 - Herd immunity conferred by killed oral cholera vaccines in Bangladesh
T2 - A reanalysis
AU - Ali, Mohammad
AU - Emch, Michael
AU - Von Seidlein, Lorenz
AU - Yunus, Mohammad
AU - Sack, David A.
AU - Rao, Malla
AU - Holmgren, Jan
AU - Clemens, John D.
N1 - Funding Information:
This paper is dedicated to the memory of Dang Duc Trach. We also thank the staff of the ICDDR,B, whose diligence and dedication were critical to the success of the trial and Taesung Park for providing valuable comments on the paper. Funding for the analysis reported in this paper was provided by the Diseases of the Most Impoverished Program of the Bill and Melinda Gates Foundation; grant number 1R03AI53214-01 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health; and grant number 0323131 of the Geography and Regional Science Program, National Science Foundation.
PY - 2005/7/2
Y1 - 2005/7/2
N2 - Background: Decisions about the use of killed oral cholera vaccines, which confer moderate levels of direct protection to vaccinees, can depend on whether the vaccines also provide indirect (herd) protection when high levels of vaccine coverage are attained. We reanalysed data from a field trial in Bangladesh to ascertain whether there is evidence of indirect protection from killed oral cholera vaccines. Methods: We analysed the first year of surveillance data from a placebo-controlled trial of B subunit-killed whole-cell and killed whole-cell-only oral cholera vaccines in children and adult women in Bangladesh. We calculated whether there was an inverse, monotonic trend for the relation between the level of vaccine coverage in a residential cluster and the incidence of cholera in individual vaccine recipients or placebo recipients residing in the cluster after controlling for potential confounding variables. Findings: Vaccine coverage of the targeted population ranged from 4% to 65%. Incidence rates of cholera among placebo recipients were inversely related to levels of vaccine coverage (7·01 cases per 1000 in the lowest quintile of coverage vs 1·47 cases per 1000 in the highest quintile; p<0·0001 for trend). Receipt of vaccine by an individual and the level of vaccine coverage of the individual's cluster were independently related to a reduced risk of cholera. Moreover, after adjustment for the level of vaccine coverage of the cluster, vaccine protective efficacy remained significant (55% [95% CI 41-66], p<0·0001). Interpretation: In addition to providing direct protection to vaccine recipients, killed oral cholera vaccines confer significant herd protection to neighbouring non-vaccinated individuals. Use of these vaccines could have a major effect on the burden of cholera in endemic settings.
AB - Background: Decisions about the use of killed oral cholera vaccines, which confer moderate levels of direct protection to vaccinees, can depend on whether the vaccines also provide indirect (herd) protection when high levels of vaccine coverage are attained. We reanalysed data from a field trial in Bangladesh to ascertain whether there is evidence of indirect protection from killed oral cholera vaccines. Methods: We analysed the first year of surveillance data from a placebo-controlled trial of B subunit-killed whole-cell and killed whole-cell-only oral cholera vaccines in children and adult women in Bangladesh. We calculated whether there was an inverse, monotonic trend for the relation between the level of vaccine coverage in a residential cluster and the incidence of cholera in individual vaccine recipients or placebo recipients residing in the cluster after controlling for potential confounding variables. Findings: Vaccine coverage of the targeted population ranged from 4% to 65%. Incidence rates of cholera among placebo recipients were inversely related to levels of vaccine coverage (7·01 cases per 1000 in the lowest quintile of coverage vs 1·47 cases per 1000 in the highest quintile; p<0·0001 for trend). Receipt of vaccine by an individual and the level of vaccine coverage of the individual's cluster were independently related to a reduced risk of cholera. Moreover, after adjustment for the level of vaccine coverage of the cluster, vaccine protective efficacy remained significant (55% [95% CI 41-66], p<0·0001). Interpretation: In addition to providing direct protection to vaccine recipients, killed oral cholera vaccines confer significant herd protection to neighbouring non-vaccinated individuals. Use of these vaccines could have a major effect on the burden of cholera in endemic settings.
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U2 - 10.1016/S0140-6736(05)66550-6
DO - 10.1016/S0140-6736(05)66550-6
M3 - Article
C2 - 15993232
AN - SCOPUS:21844472531
SN - 0140-6736
VL - 366
SP - 44
EP - 49
JO - Lancet
JF - Lancet
IS - 9479
ER -