Assessment of shed OPV from infants

Sabin strains used in oral poliovirus vaccine (OPV) can revert to virulence and in rare instances cause disease or generate vaccine-derived strains leading to outbreaks in areas of poor immunization coverage. A novel OPV2 (nOPV2) was designed to stabilise the viral genome against reversion and also reduce recombination events that may lead to virulent strains. In two similarly designed clinical trials, 18-22-week-old infants, after full immunisation with three doses of bivalent OPV (types 1 and 3) and one dose of inactivated poliovirus vaccine (IPV), were administered one or two doses of monovalent Sabin OPV2 (mOPV2) or nOPV2. Faecally shed polioviruses following a dose of mOPV2 or nOPV2 were isolated from stools meeting pre-determined criteria and assessed for nucleotide polymorphisms using next-generation sequencing.