Polio, which was officially eradicated in the UK in 2003, can cause paralysis, and in rare cases, it can also be life-threatening.
While there have been no confirmed cases, officials have raised the alarm over the rising number of samples found in London sewage.
The UK Health Security Agency (UKHSA), which works with the Medicines and Healthcare products Regulatory Agency (MHRA), found poliovirus in sewage samples from the London boroughs of Barnet, Brent, Camden, Enfield, Hackney, Haringey, Islington and Waltham Forest.
It was first detected at Beckton sewage treatment works earlier this year.
Here’s everything you need to know.
Where in London has the virus been detected?
Poliovirus has been found in sewage samples from the London boroughs of Barnet, Brent, Camden, Enfield, Hackney, Haringey, Islington and Waltham Forest.
How was the virus discovered?
Sewage from Beckton sewage works is tested fortnightly to check for various diseases. The virus was first detected in February, then again in April and also more recently. The samples were found to have genetic similarities, leading to the belief that a family or extended family is involved.
How worried should we be?
Health chiefs say the discovery is of “concern but the current risk [of the virus spreading] is low”. About 15 per cent of London teenagers have not had their two boosters. It is children and teenagers who are unvaccinated that are at risk.
What is polio?
Polio is a rare disabling and life-threatening disease caused by the poliovirus. It can affect the limbs or the respiratory and nervous system.
The virus multiplies in the intestine and infected people excrete large quantities of virus in their faeces. The virus can infect a person’s spinal cord, causing paralysis.
Does everybody who gets polio become seriously ill?
No. Most people with polio won’t have any symptoms and will fight off the infection without even realising they were infected. A small number of people will experience a flu-like illness three to 21 days after being infected.
In a small number of cases, between one in 100 to one in 1000 infections, the polio virus attacks the nerves in the spine and base of the brain. This can cause paralysis, usually in the legs, that develops over hours or days. If the breathing muscles are affected, it can be life threatening.
What are the symptoms of polio?
Symptoms can include: high temperature (fever) of 38C or above; sore throat; headache; abdominal pain; aching muscles; feeling or being sick. These symptoms will usually pass within about a week without any medical intervention.
Wasn’t polio a disease from the 1940s and 1950s?
Yes, certainly in the UK at least. In the 1940s there were around 2,000 cases a year, and there were large outbreaks in the 1940s and 1950s. This led to the UK to introduce an injectable vaccine in 1955, which was switched to an oral vaccine in 1961. Many adults will recall receiving it on a sugar lump at school. The UK switched back to an injectable vaccine in 2004 and it is now given as part of the six-in-one jab to babies, over three doses, followed by boosters for pre-school children and teenagers. Polio is officially eradicated in the UK but the current virus has been imported.
Where did the polio virus come from?
It is thought to have been shed in the faeces of a person recently arrived in the UK. That person would have received the oral vaccine abroad, and parts of the “live” virus will have been transferred - probably through poor hygiene practices, such as not washing hands after using the loo and then touching food eaten by others.
How many people are infected?
It is impossible to say at this stage - experts cannot be sure how many cases of virus are required to enable it to be detected in sewage sampling. But it is thought to be an extended family rather than hundreds or thousands of people. “very small numbers” is the best guestimate at present.
Has anyone developed polio as a result?
No. There have been no reported cases to date. The overall risk to the public is classified as “low”.
Is there a link to the pandemic - or the war in Ukraine?
Yes and no. It is known that the school vaccination programme has fallen behind schedule due to the various lockdowns, and children being away from the classroom. However the poliovirus that has been detected in London is not the same virus as has been found in the Ukraine.
What can I do to protect my children against polio?
Check their vaccine records and if they have not had all three doses (given to babies at eight, 12 and 16 weeks as part of the six-in-one vaccine) and the pre-school (age three years and four months) and teenage boosters (age 14), contact your GP.
Any more details about the virus?
It has been classified as a “vaccine-derived” poliovirus type 2 (VDPV2), which on rare occasions can cause serious illness, such as paralysis, in people who are not fully vaccinated.
Who discovered the virus?
The testing was conducted by the WHO Global Specialised Polio Laboratory located at the National Institute for Biological Standards and Control, which is part of the Medicines and Healthcare products Regulatory Agency (MHRA). The centre con-ducts routine environmental surveillance for wild type and vaccine-like polioviruses as part of the UK’s commitment to the WHO global polio eradication programme.
How do viruses spread?
Vaccine viruses can spread in under-vaccinated communities from person to person through poor hand hygiene and water and food contamination (and, less frequently, through coughs and sneezes).
During the spread the virus can mutate into a “vaccine-derived poliovirus’”. This behaves more like naturally occurring “wild” polio and may, on rare occasions, lead to cases of paralysis in unvaccinated individuals.