Polio is a serious viral infection that used to be common all over the world.
The virus lives in the throat and intestines for up to six weeks, with patients most infectious from seven to 10 days before and after the onset of symptoms.
But it can spread to the spinal cord causing muscle weakness and paralysis.
The virus is more common in infants and young children and occurs under conditions of poor hygiene.
How deadly is it?
Most people show no signs of infection at all but about one in 20 people have minor symptoms such as fever, muscle weakness, headache, nausea and vomiting.
Around one in 50 patients develop severe muscle pain and stiffness in the neck and back.
Less than one per cent of polio cases result in paralysis and one in 10 of those result in death.
Of those who develop symptoms, these tend to appear three-to-21 days after infection and include:
- High temperature
- Sore throat
- Abdominal pain
- Aching muscles
- Nausea and vomiting
How does it spread?
People can catch polio via droplets in the air when someone coughs or sneezes, or if they come into contacted with the faeces of an infected person.
This includes food, water, clothing or toys.
Are there different strains?
There are three strains of ‘wild’ polio, which has been largely eradicated throughout Europe, the Americas, Southeast Asia and the Western Pacific.
Types 2 and 3 were eliminated thanks to a global mass vaccine campaign, with the last cases detected in 1999 and 2012 respectively.
The remaining, type 1, wild polio remains endemic in only two countries, Afghanistan and Pakistan.
Wild polio has been eliminated in almost every country in the world thanks to vaccines.
But the global rollout has spawned new types of strains known as vaccine-derived polioviruses.
These are strains that were initially used in live vaccines but spilled out into the community and evolved to behave more like the wild version.
Is polio still around in the UK?
The last polio outbreak was in the 1970s.
The last case of person-to-person transmission in the UK was in 1984, which also marked the last wild polio case.
But there have been several dozen cases of vaccine-derived polioviruses, although they have been one-offs, with no onward transmission.
Am I vaccinated against polio?
The polio vaccine is offered as part of the NHS routine childhood vaccination programme.
It is given at age eight, 12 and 16 weeks as part of the six-in-one vaccine and then again at three years as part of a pre-school booster. The final course is given at age 14.
Uptake has fallen slightly nationally during the Covid pandemic but remains above 90 per cent nationally. Rates are lower in London and in poor and ethnic minority communities.
Just 86.7 per cent of one-year-olds in London have had their first dose dose of polio vaccine compared to the UK average of 92.6 per cent.
There are concerns vaccine hesitancy has risen during the Covid crisis due to misinformation spread about jabs for that virus and school closures.