The emergence of circulating vaccine-derived polioviruses through evolution of the oral polio vaccine (OPV) poses a significant obstacle to polio eradication. Understanding the early genetic changes that occur as OPV evolves and transmits is important for preventing future outbreaks. Here, we use deep sequencing to define the evolutionary trajectories of type 2 OPV in a vaccine trial. By sequencing 497 longitudinal stool samples from 271 OPV2 recipients and household contacts, we were able to examine the extent of convergent evolution in vaccinated individuals and the amount of viral diversity that is transmitted. In addition to rapid reversion of key attenuating mutations, we identify strong selection at 19 sites across the genome. We find that a tight transmission bottleneck limits the onward transmission of these early adaptive mutations. Our results highlight the distinct evolutionary dynamics of live attenuated virus vaccines and have important implications for the success of next-generation OPV. Display omitted •We used deep sequencing to define the evolutionary trajectories of type 2 OPV•We identified strong positive selection at multiple, non-attenuating sites•Transmission bottleneck limits spread of variants that are selected within hosts•This work provides insights into the evolution of live attenuated virus vaccines The emergence of vaccine-derived polioviruses through evolution of the oral polio vaccine poses a significant obstacle to global poliovirus eradication. Valesano et al. use sequencing of samples from vaccine recipients and household contacts to identify multiple mutations that are selected within hosts. Tight bottlenecks limit the onward transmission of these variants.