The Maldonado Group recently received a grant from the Bill & Melinda Gates Foundation for a 2.5 year study investigating the dynamics of oral poliovirus vaccine (OPV) household and community transmission in 3 communities in Orizaba, Veracruz, Mexico. Mexico provides a unique environment to study OPV transmission. Currently, Mexican children receive inactivated poliovirus vaccine (IPV) in their primary vaccination series. In addition, children ≤5 years old who have received at least 2 doses of IPV are eligible to receive OPV during biannual National Immunization Weeks. Our study will specifically assess the impact of different OPV vaccination rates during the February 2015 National Immunization Week on intra- and inter-household transmission of OPV. The outcome of this project will inform public policy decision-making regarding OPV cessation and the polio end-game.