Alongside the wild-type outlined above, there are also rare cases of what is known as vaccine-derived polio.
It is this second form detected in wastewater in the British capital, London, and in New York in the United States, with one case of paralysis reported in New York state.While vaccine-derived polio is almost unheard of in the above locations, it is a known - albeit rare - threat in other countries, causing outbreaks every year, including 415 cases in Nigeria in 2021.It stems from the use of an oral polio vaccine containing weakened live virus.While countries including the Britain and the United States no longer use this live vaccine, others do - particularly to stop outbreaks - which allows for global spread, particularly as people began to travel again after COVID-19, experts said.But experts agree that the major driver behind both vaccine-derived and wild polio outbreaks remains under-vaccinated populations, said Derek Ehrhardt, global polio lead at the United States Centers for Disease Control and Prevention (CDC).In 2020, there were 1,081 vaccine-derived polio cases, around three times as many as the previous year.