The oral vaccine is cheaper, easier to administer and induces stronger intestinal immunity that blocks transmission, which made it the workhorse of the global eradication campaign; but its live virus can, rarely, revert to a form that causes circulating vaccine-derived poliovirus (cVDPV) outbreaks, 721 cases of which were reported worldwide between January 2005 and May 2016, 94 percent of them from the vaccine's own type 2 component. The injected inactivated vaccine carries no such reversion risk but is costlier, requires trained staff to administer, and confers weaker intestinal immunity. The World Health Organization coordinated a global, synchronized switch from trivalent to bivalent oral vaccine in April 2016 specifically to retire the type 2 oral component, introducing injected vaccine into routine schedules worldwide to cover the resulting gap, a policy tradeoff public health authorities continue to weigh as wild poliovirus nears eradication in the remaining endemic countries.
What would resolve this Sustained, verified interruption of all wild and vaccine-derived poliovirus transmission worldwide following a specific vaccine strategy, or a WHO Strategic Advisory Group of Experts consensus settling the remaining oral-to-inactivated transition timeline.
OpenPublic Health and EpidemiologyCDC MMWR: Introduction of Inactivated Poliovirus Vaccine and Switch from Trivalent to Bivalent Oral Poliovirus Vaccine