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 .
Improving immunisation coverage in rural India: clustered randomised controlled evaluation of immunisation campaigns with and without incentives
Objective To assess the efficacy of modest non-financial incentives on immunisation rates in children aged 1 - 3 and to compare it with the effect of only improving the reliability of the supply of services . Design Clustered r and omised controlled study . Setting Rural Rajasthan , India . Participants 1640 children aged 1 - 3 at end point . Interventions 134 villages were r and omised to one of three groups : a once monthly reliable immunisation camp  ( intervention A ; 379 children from 30 villages ) ; a once monthly reliable immunisation camp with small incentives ( raw lentils and metal plates for completed immunisation ;  intervention B ; 382 children from 30 villages ) , or  control ( no intervention , 860 children in 74 villages ) . Surveys were undertaken in r and omly selected households at baseline and about 18 months after the interventions started ( end point ) . Main outcome measures Proportion of children aged 1 - 3 at the end point who were partially or fully immunised . Results Among children aged 1 - 3 in the end point survey , rates of full immunisation were 39 % ( 148/382 , 95 % confidence interval 30 % to 47 % ) for intervention B villages ( reliable immunisation with incentives ) , 18 % ( 68/379 , 11 % to 23 % ) for intervention A villages ( reliable immunisation without incentives ) , and 6 % ( 50/860 , 3 % to 9 % ) for control villages . The relative risk of complete immunisation for intervention B versus control was 6.7 ( 4.5 to 8.8 ) and for intervention B versus intervention A was 2.2 ( 1.5 to 2.8 ) . Children in areas neighbouring intervention B villages were also more likely to be fully immunised than those from areas neighbouring intervention A villages ( 1.9 , 1.1 to 2.8 ) . The average cost per immunisation was $ 28 ( 1102 rupees , about £ 16 or € 19 ) in intervention A and $ 56 ( 2202 rupees ) in intervention B. Conclusions Improving reliability of services improves immunisation rates , but the effect remains modest . Small incentives have large positive impacts on the uptake of immunisation services in re source poor areas and are more cost effective than purely improving supply . Trial registration IRSCTN87759937
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 .