The world is fast approaching the largest globally synchronised project in the history of vaccines. Between 17 April and 1 May 2016, every country in with world using the oral polio vaccine (OPV) will switch from the trivalent vaccine (tOPV), which protects children against all three types of the virus, to the bivalent vaccine which protects children against type one and three. Now that type two wild polio has been declared eradicated, this is an essential part of the work that needs to be done to secure a polio-free world by phasing out oral polio vaccines to prevent future outbreaks of vaccine-derived polioviruses.