Polio Endgame, Information Gaps Related to Vaccines and Immunity.

Evidence generated through research studies has guided programmatic actions and fine-tuned strategies for the Global Polio Eradication Initiative (GPEI). However, many gaps still persist in the understanding of a risk-free implementation of the polio endgame. Immediate concerns relate to the introduction of inactivated polio vaccine (IPV) and switch from trivalent oral polio vaccine (tOPV) to bivalent oral polio vaccine (bOPV) in routine immunization schedule. A comprehensive understanding of mucosal immunity in populations and best response options against circulating vaccine derived poliovirus (cVDPV) outbreaks in post tOPV-bOPV switch is essential to mitigate the risks of wild and vaccine-derived poliovirus importations and emergence of cVDPVs in polio-free countries. A clearer picture is also needed on few operational issues, interference between polio vaccines and other EPI vaccines and products related to polio endgame. It is also extremely important to develop mechanisms to identify and manage long-term poliovirus excretors who may pose a risk of reintroduction into the population after global eradication of poliovirus.