He had an immune disorder that mean the weakened polio virus used to vaccinate him in childhood survived in his body.
Over time it has mutated into a form of the virus that can cause paralysis and he had no idea the jab had not worked.
Polio is only endemic in Pakistan, Afghanistan and Nigeria although Nigeria has now gone more than a year without a case.
The discovery was made by a team from the National Institute for Biological Standards and Control in Potters Bar, Hertfordshire.
They now warn that similar cases could trigger new outbreaks and hamper efforts to eradicate the disease.
They wrote in the journal PLOS Pathogens: “While maintaining high immunisation coverage will likely confer protection against paralytic disease caused by these viruses, significant changes in immunisation strategies might be required to effectively stop their occurrence and potential widespread transmission.”
The man had a full course of polio vaccinations, including three doses of weakened live virus at five, seven and 12 months old, followed by a booster when he was about seven.
He was later diagnosed with a condition that suppresses the immune system, affecting its ability to kill viruses in the gut.
His stool samples contained high levels of polio virus…
