We will collect stool samples from all members of the enrolled households serially over the course of the study and will determine if individuals shed OPV in their stool using a serotype-specific real-time polymerase chain reaction (PCR) assay. We will define inter-household transmission as fecal OPV shedding by any member of a non-vaccinated household. By comparing inter-household transmission rates among all the household clusters, we will determine the if the proportion of OPV-vaccinated children impacts community OPV transmission in a primarily IPV-vaccinated community. These results will be critical to predicting the risk of OPV re-introduction in the event of a poliomyelitis outbreak in the post-OPV era.