Live oral poliovirus vaccines (OPVs) are known to be safe and effective and have led to the elimination of polio from most of the world. However, in rare circumstances the attenuated viruses in OPVs can mutate and reacquire virulence. This can result in vaccine-associated paralytic polio and lead to the emergence of circulating vaccine-derived polioviruses (cVDPVs), particularly in settings with poor immunisation coverage. View More