OPV Transmissibility in Communities After Cessation of Routine OPV Immunization

The investigators propose to study both inter- and intra-household Oral Polio Vaccine (OPV) transmission in a primarily inactivated-polio vaccine (IPV)-vaccinated community in Mexico. The investigators will enroll 3 distinct clusters of households in a municipality in Orizaba, Veracruz, Mexico prior to the February 2015 National Immunization Week (NIW.) These clusters will be physically separate from one another and differ only in the proportion of OPV-eligible children who will receive OPV during the February 2015 NIW (10%, 30% and 70% vaccinated.) The investigators will look at inter-household and intra-household transmission. The investigators will then determine if epidemiologic (i.e.: degree of contact), anthropometric (i.e.: nutritional status) or clinical covariates (i.e.: IPV/OPV immunization history) are associated with intra-household transmission.