More Vaccine-Derived Cases as Fight Against Polio Progresses

Cheap and easy-to-administer oral polio vaccines have been the key to diminishing cases of the disease globally by 99 percent since the 1950s. A side effect has been the emergence of vaccine-derived polio, which originates from excreted and mutated polio vaccine remnants. Today there are more polio cases of this type than of wild polio, but still far fewer than in previous decades.

In 2024, 99 wild polio cases occured, all of them in Pakistan and Afghanistan, the only two countries where the disease is still endemic. The number of vaccine-derived polio cases was higher last year, at 562 occuring in Ethiopia, Nigeria, Yemen and several other countries in Africa, Asia and the Pacific. As recently as 1993, global polio cases had still exceeded 10,000, however.

Like all polio viruses, the vaccine-derived type is only really dangerous to undervaccinated persons and populations. Sufficient vaccination coverage can protect from these and other infections, while improved oral vaccines and polio shots are also expected to mitigate the risk of emerging polio strains in the future. In 2024, vaccine-derived polio started to spread in Gaza, showing how disruptions due to conflict can expose populations to polio once vaccine coverage and the access to proper hygiene facilities sinks.