Research in context
infection
INFECTION, PARALYTIC POLIOMYELITIS, POLIO

Outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2) are now the main cause of paralytic poliomyelitis worldwide. A novel, genetically more stable monovalent type 2 oral polio vaccine that was developed for use in outbreak control with less inherent chance of propagating more cVDPV2 has been studied in clinical trials involving infants, children, adolescents, and adults previously primed with at least one dose of type 2-containing poliovirus vaccine and shown to be safe, well tolerated, and immunogenic. On the basis of this clinical evidence, WHO authorised the use of a novel oral poliovirus vaccine type 2 (nOPV2) for outbreak control through the emergency use listing (EUL) procedure and more than 450 million doses have been distributed for use since March 2021. However, no clinical trial data are available for the use of nOPV2 in poliovirus vaccine-naive infants, who are at particular risk of infection during cVDPV2 outbreaks.
The EUL-enabling clinical data on nOPV2 included safety and immunogenicity data in infants who had already received a dose of inactivated poliovirus vaccine. Thus, generating vaccine performance data in poliovirus vaccine-naive infants or newborn babies was important to complete the clinical database on the new vaccine. Moreover, the highest-risk groups in cVDPV outbreaks are those with incomplete or no poliovirus vaccination such as newborn and very young infants. These groups will be priority targets in vaccination campaigns with nOPV2 for cVDPV2 outbreak control. Our data showing that nOPV2 is safe, well tolerated, and immunogenic in newborn infants are important for those health-care administrators and decision makers responsible for implementing such campaigns as well as being reassuring for the parents and carers of affected children. Equally important is our observation that nOPV2 use in newborn infants will not lead to excessive faecal excretion of live nOPV2, further minimising the risks of propagating a cVDPV2 outbreak.
Since WHO declared that cVDPV2 outbreaks are a public health emergency of international concern and following submission of earlier clinical data on nOPV2 in individuals aged at least 18 weeks to adults, WHO authorised the distribution and use of the vaccine in such outbreaks as the first vaccine to be used under the EUL process. To date, more than 450 million doses of nOPV2 have been distributed and have been used in all age groups targeted for outbreak response with no exclusion of use in newborn infants. The data from this study can inform policy makers, regulators, and health-care providers that the use of nOPV2 in poliovirus vaccine-naive newborn infants, the age group considered most vulnerable for poliovirus transmission, is safe and immunogenic.The clinical development of nOPV2 is ongoing, but the successful demonstration of its safety, immunogenicity, and genetic stability in phase 1 and phase 2 studies coupled with the public health emergency of international concern constituted by cVDPV2 outbreaks led to the authorisation by WHO of the vaccine's use under WHO's emergency use listing (EUL) procedure. To date, over 450 million doses have been distributed for outbreak control.