STORY: (GFX: Why has polio returned to the United States?)Polio has returned, spreading in London, Jerusalem and New York for the first time in decades.In July, a case of polio in an adult was made public in Rockland County, New York.It marks the nation's first confirmed case in nearly 10 years.Later in August, health officials said the virus was found in New York City’s wastewater.So just how dangerous is the disease?(GFX: Dreaded disease)Polio terrified parents around the world for the first half of the 20th century.Affecting mainly children under five, polio is often asymptomatic but can also cause symptoms including fever and vomiting.Around one in 200 infections leads to irreversible paralysis.And among those patients, up to 10% die.The disease spreads mainly through contact with faecal matter.There is no cure, but polio is entirely preventable through vaccination.Globally, the wild form of the disease has almost disappeared.Afghanistan and Pakistan are now the only countries where the disease remains endemic.(GFX: Different strains)There are two main forms of poliovirus.The wild-type and rare cases of what is known as vaccine-derived polio.It’s the second form that was detected in wastewater in New York, with one case of paralysis reported in the state.Rockland County Health Commissioner Patricia Schnabel Ruppert.(GFX: Vaccine-derived polio)Vaccine-derived polio has also recently been detected in London and Jerusalem.It stems from the use of an oral polio vaccine containing weakened live virus.After vaccination, children shed bits of the virus in their faeces for a few weeks.In under-vaccinated communities, this can spread and mutate back to a harmful version of the virus.While countries like Britain and the U.S. no longer use this live vaccine, others do, which allows for global spread, particularly as people began to travel again after COVID.(GFX: Why now?)Experts agree that the major driver behind both vaccine-derived and wild polio outbreaks remains under-vaccinated populations.Vaccine hesitancy was a growing problem before the pandemic and then COVID-19 caused the worst disruption to routine immunization in a generation. That’s according to the United Nations.In 2020, there were 1,081 vaccine-derived polio cases.That’s around three times as many as the previous year.In 2022, there have been 177 cases so far, after major efforts to get polio vaccination campaigns back on track.Health experts say the New York City wastewater findings are still a wake-up call for parents,with one key message: protect your children by getting them vaccinated.