It is exceedingly rare for the public health community to admit to any problems with vaccination.
Every so often, however, circumstances force officials into making just such an acknowledgment.
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.
Researchers concede that an OPV virus “can very rapidly regain its strength if it starts spreading on its own,” acquiring “mutations that make it basically indistinguishable from the wild-type virus.” In other words, there is no meaningful difference between a wild and OPV-derived poliovirus “in terms of virulence and in terms of how the virus spreads.”