BLANTYRE, Malawi — In a classroom in southern Malawi, children sit in rows on the floor as a health worker moves among them administering an oral vaccine that protects against polio.
The new vaccination campaign that began on Wednesday is another reminder that the world still hasn't managed to eradicate the ancient disease, which primarily affects children and can cause paralysis, despite a concerted effort for more than 35 years by the World Health Organization and its partners.
Health officials believe they came close several times, including five years ago, when just five cases of the natural polio virus were reported globally.
But a WHO report said that there were 38 cases of the natural polio virus between January and October 2025 — all in Pakistan and Afghanistan, the last two countries where it remains endemic — and another 151 cases of a vaccine-derived polio virus strain in 13 countries.
Vaccines caused some cases
Those vaccine-derived cases have overtaken natural polio virus cases in recent years, and complicated the eradication effort as one of a number of missteps in the global fight. They come about when the weakened live virus in oral polio vaccines mutates into a form capable of sparking new outbreaks.
That's the problem in Malawi, which reported last month that it had discovered the vaccine-derived Type 2 polio virus strain in sewage water in the southern city of Blantyre, prompting health authorities to launch a new immunization campaign using a modified vaccine.
By WHO regulations, Malawi was required to declare an outbreak on confirming the polio virus traces.