In a small number of cases, the polio virus attacks the nerves in the spine and base of the brain, which can cause paralysis, usually in the legs, that develops over hours or days, says the NHS.
“The paralysis isn’t usually permanent, and movement will often slowly return over the next few weeks and months,” explained the health body.
It added: “But some people are left with persistent problems. If the breathing muscles are affected, it can be life threatening.”
Although polio often passes quickly without causing any other problems, it can sometimes lead to persistent or lifelong difficulties, as in Mary’s case.