The current debacle seeping out into the news—which is actually a long-running tale minted anew—is that oral polio vaccines are "spawning virulent strains" of polioviruses. The alarming surge in vaccine-derived polio cases presents vaccine planners with a "quandary" or "conundrum"—because "The very tool you are using for [polio] eradication is causing the problem."
The oral polio vaccine (OPV) is in use around the world and constitutes the "workhorse" of global polio eradication efforts due to its low cost and ease of administration. The OPV contains live but weakened polioviruses that match up to wild polioviruses. Vaccine researchers have long known that these OPV-derived viruses can themselves cause polio, particularly when they get "loose in the environment." In settings with poor sanitation and iffy hygiene, the vaccine viruses can easily "find their way into water sources, and onto contaminated hands or foods," where they can then launch a self-perpetuating chain of transmission.