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 .
Components of the indirect effect in vaccine trials: identification of contagion and infectiousness effects.
Vaccination of one person may prevent the infection of another either because the vaccine prevents the first from being infected and from infecting the second , or because , even if the first person is infected , the vaccine may render the infection less infectious . We might refer to the first of these mechanisms as a contagion effect and the second as an infectiousness effect . In the simple setting of a r and omized vaccine trial with households of size two , we use counterfactual theory under interference to provide formal definitions of a contagion effect and an unconditional infectiousness effect . Using ideas analogous to mediation analysis , we show that the indirect effect ( the effect of one person 's vaccine on another 's outcome ) can be decomposed into a contagion effect and an unconditional infectiousness effect on the risk difference , risk ratio , odds ratio , and vaccine efficacy scales . We provide identification assumptions for such contagion and unconditional infectiousness effects and describe a simple statistical technique to estimate these effects when they are identified . We also give a sensitivity analysis technique to assess how inferences would change under violations of the identification assumptions . The concepts and results of this paper are illustrated with hypothetical vaccine trial data
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 .