We identified three primary mechanisms of spillovers : reduced disease transmission , social proximity and substitution of re sources within households .
We found the strongest evidence for spillovers through reduced disease transmission , particularly vaccines and mass drug administration .
In general , the proportion of a population receiving an intervention was associated with improved health .
We found evidence of publication bias for certain spillover estimates but not for total or direct effects .
Conclusions We found the strongest evidence for spillovers from vaccines and mass drug administration to control infectious disease .
There was little high quality evidence of spillovers for other interventions
Background Many interventions delivered to improve health may benefit not only direct recipients but also people in close physical or social proximity .
Our objective was to review all published literature about the spillover effects of interventions on health outcomes in low-middle income countries and to identify methods used in estimating these effects .
Herd protection by a bivalent killed whole-cell oral cholera vaccine in the slums of Kolkata, India.
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-r and omized 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 non participants 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 . CLINICAL TRIALS REGISTRATION NCT00289224
We identified three primary mechanisms of spillovers : reduced disease transmission , social proximity and substitution of re sources within households .
We found the strongest evidence for spillovers through reduced disease transmission , particularly vaccines and mass drug administration .
In general , the proportion of a population receiving an intervention was associated with improved health .
We found evidence of publication bias for certain spillover estimates but not for total or direct effects .
Conclusions We found the strongest evidence for spillovers from vaccines and mass drug administration to control infectious disease .
There was little high quality evidence of spillovers for other interventions
Background Many interventions delivered to improve health may benefit not only direct recipients but also people in close physical or social proximity .
Our objective was to review all published literature about the spillover effects of interventions on health outcomes in low-middle income countries and to identify methods used in estimating these effects .