Within-host diversity of monovalent OPV2 in vaccine recipients and household contacts

Polio vaccines are essential tools for prevention of poliomyelitis. However, the transmission and evolution of the oral polio vaccine (OPV) poses an obstacle to complete global eradication. Examining how OPV evolves at the level of individual hosts can shed light on the development of cVDPV in larger populations. We use genome sequencing to assess the early evolution of monovalent OPV type 2 in a cluster-randomized trial of polio vaccines conducted in Matlab, Bangladesh. We provide a detailed characterization of the fixation rates of mutations known to contribute to reversion to virulence and identify other mutations that arise in multiple vaccine recipients. We show that these critical reversion mutations are not always transmitted to household contacts of vaccine recipients, consistent with a relatively tight between-host bottleneck. Our findings provide important insights into how OPV genetic variants spread in populations and data that will be important for ongoing genetic surveillance for polioviruses.