A mutated virus, anti-vaxxers and a vulnerable population: how polio returned to the US

In July, a young man in the New York are was diagnosed with polio - how did a disease America snuffed out in the 70s rebound?

This June, a young man from Rockland county, New York went to the emergency room. He'd been feverish for five days and was suffering from a stiff neck, pain in his back and abdomen, and constipation. Even more concerning, for two days his legs had been abnormally weak. Doctors suspected the man had acute flaccid myelitis - muscle weakness caused by inflammation of the spinal cord, typically stemming from a viral infection. Lab tests revealed a shocking diagnosis: the culprit was the poliovirus.

Throughout the first half of the 20th century, thousands of children died or were paralyzed due to polio; there were 20,000 cases of polio-induced paralysis in 1952 alone. Polio's eradication from the US in 1979 thanks to vaccines is one of the greatest achievements of modern medicine. In the 21st century, there had been just three known instances of polio in the US - all thought to be imported - affecting a total of 10 people, with only one involving community spread.