Children in the UK aged one to nine are now to to be offered a dose of polio vaccine, which may be a booster or may bring them up to date with routine vaccinations.
Regardless of where they are on their vaccine schedule, they will be offered the immunisation in Greater London as a preventative measure due to signs of the virus spreading in the capital.
"No cases of polio have been reported and for the majority of the population, who are fully vaccinated, the risk is low," said Dr Vanessa Saliba, Consultant Epidemiologist at the UK Health Security Agency.
"But we know the areas in London where the poliovirus is being transmitted have some of the lowest vaccination rates. This is why the virus is spreading in these communities and puts those residents not fully vaccinated at greater risk." The virus has been found in the city's sewage system recently.
The last case of polio in the UK was in 1984, but before the vaccination programme was introduced (in 1965) some 8,000 people would develop paralysis (one of the more serious symptoms) every year, according to Saliba.
What is polio?
While polio is a serious infection, it's now very rare because of the vaccination programme. The chances of getting it in the UK is extremely low and it's only found in a few countries.
Also known as poliomyelitis, it can be a life-threatening illness caused by the poliovirus, which can cause debilitating symptoms.
How does polio spread?
Polio spread from person to person, usually through contact with the poo of an infected individual, according to the NHS.
It might be from not washing your hands properly and touching your mouth, or from contaminated food and water.
While less common, it can also spread through coughs or sneezes.
Polio was eradicated in Europe in 2003, but as there have been signs of it in London, boosting immunity in children should help to stop it from spreading any further.
There's also only a small risk of catching it when travelling in countries where polio is found, like Afghanistan or Pakistan.
Polio can be hard to detect as most people who contract it don't have symptoms.
However, as per the health service, some people get the following mild, flu-like symptoms:
a high temperature
extreme tiredness (fatigue)
being sick (vomiting)
a stiff neck
These symptoms will typically only last for up to 10 days.
However, in more rarer cases, it can lead to more severe symptoms that can affect the brain and the nerves. This might cause weakness in your muscles, which is what is referred to as paralysis, often in the legs, which can occur for a few hours or days.
Paralysis that affects muscles used for breathing can be life threatening.
While most people will recover and slowly regain movement, some can be left with permanent disability.
If you've already had polio, you might develop symptoms again or your symptoms might get worse years later, which is called post-polio syndrome.
While there is no official treatment for polio, bed rest in hospital, painkillers, help with breathing and regular stretches and exercises can help.
Prevention is the best cure, which is why it's important to make sure both you and you child are up to date with your polio vaccinations.
When to get help
Contact your GP if you are unsure about any symptoms. The NHS also advises contacting 111 if you have flu-like symptoms and you're worried about a baby's or child's symptoms, you're 65 or over, you're pregnant, you have a long-term health condition, you have a weak immune system or your symptoms don't improve after a week.
Call 999 or go to A&E if you or your child isn't able to move part, or all, of the body, or it feels stiff, floppy or numb, or you are having difficulty breathing or are breathless.
Watch: Dr Ramsay encourages polio vaccination after samples found