What is polio and why is it back?

Health authorities in the UK have declared a national incident after polio virus was detected in sewage samples collected at the London Beckton Sewage Treatment Works.

In February, sewage from the treatment works in Newham, east London, which processes waste from 4 million people in north and east London, produced a positive test for polio virus. Usually this would not be a cause for concern but tests in April revealed a genetically related polio virus which has continued to evolve.

This raises concern that the infection could spread and cause harm, particularly in unvaccinated young children who could become paralysed from the virus.

Investigations are underway to protect the public, who have been urged to ensure their polio vaccines are up to date, especially for parents of young children who may have missed an immunisation opportunity.

While health authorities have said that the use of the term “national incident” was used to explain the scope of the issue, no cases of polio have been identified so far, and risk to the general public remains low. 

What is polio?

Polio, otherwise known as poliomyelitis, is a highly-infectious, disabling and, in some cases, life-threatening disease caused by the polio virus, according to the US Centers for Disease Control and Prevention (CDC).

It primarily affects those under the age of five. After mass vaccination programmes across the 20th century, the disease is rare across most of the world, with cases remaining in Afghanistan, Nigeria and Pakistan.

What are the symptoms?

The CDC explains that most people who get infected (72 out of 100) will not have any visible symptoms, while about 1 in four will have flu-like symptoms, including a sore throat, fever, fatigue, nausea, headache or stomach pain.

These symptoms typically last two to five days and then go away on their own.

However, polio can be much more severe. Less than one out of 100 with a poliovirus infection may develop serious symptoms affecting the brain and spinal cord. This can lead to paresthesia, a feeling of pins and needles in the legs, meningitis, an infection which covers the spinal cord and/or brain in about one out of 25 people with poliovirus infection, and paralysis or weakness in the arms, legs, or both. This occurs in around 1 out of 200 people with poliovirus infection.

Paralysis, while the rarest symptom, is also the most severe, leading to permanent disability and, in some cases, death. Paralysis caused by polio can lead to death as the virus impacts the muscles that help people breathe.

Post-polio syndrome may also occur in children who once had polio, causing muscle pain, weakness, difficulty swallowing (dysphagia) or even paralysis as adults, up to 15 to 40 years after the first infection.

Why is polio back?

The UK was declared polio-free in 2003, with the last “wild polio” case confirmed in 1984.

The World Health Organization (WHO) considers the UK to be polio-free, with a low risk for polio transmission due to the high vaccine coverage across the population. 

However, vaccine coverage for childhood vaccines has decreased nationally, particularly over the last few years in parts of London. 

The UK Health Security Agency (UKHSA) is urging people to check their vaccines are up to date.

How was it detected?

Health officials analyse samples of sewage from London and Glasgow biweekly.

As part of this routine sewage surveillance, it is normal for one to three ‘vaccine-like’ unrelated cases of polio viruses to be picked up and detected each year across UK samples. 

Typically these have been one-off findings that were not detected again, coming from people who received the live oral polio vaccine (OPV) abroad and, on return or during travel to the UK, have briefly ‘shed’ traces of the vaccine-like poliovirus in their faeces.

Investigations are now underway after several closely-related viruses were found in sewage samples taken between February and May, and wastewater surveillance has been expanded to assess the risk and extent of potential transmission and to identify areas where action may be needed.

 The virus has continued to evolve and is now classified as a ‘vaccine-derived’ polio virus type 2 (VDPV2). On rare occasions, this may cause serious illness, such as paralysis, in people who are not fully vaccinated.

People who are given the oral type of polio vaccine can shed the weakened virus for weeks afterwards. On some occasions, this shed virus can spread, causing outbreaks of “vaccine-derived” poliovirus. These viruses have lost mutations that weaken them, making them more like the original poliovirus found in nature.

The detection of this type of poliovirus suggests a spread between closely-linked people in North and East London who are now shedding the VDPV2 strain in their faeces. 

So far, the virus has only been detected in sewage samples, and no associated cases of paralysis have been reported. Investigations aim to establish if any community transmission has happened or is occurring.

Healthcare workers are being asked to remain vigilant and report anyone presenting with symptoms that could be polio. Still, so far, no cases of polio or related paralysis have been reported in the UK.

Concerns remain that the vaccine-derived poliovirus could gain a foothold in areas with low vaccination rates.

How is polio transmitted and how do you catch it?

The virus is highly infectious and can spread from person to person via contact with the faeces of an infected person or droplets from a sneeze or cough (this is less common).

Polio lives in the infected personal throat and intensities and can remain there for many weeks, potentially contaminating food and water in unsanitary conditions. You may get infected with poliovirus if you pick up small amounts of faeces on your hands and touch your mouth or put contaminated items, such as toys, into your mouth.

An infected person can spread the virus to others before and up to two weeks after symptoms first appear.

Prevention

Two types of vaccines can be given to prevent polio.

The first is inactivated poliovirus vaccine (IPV) which is given as an injection in the leg or arm, depending on the patient’s age, and the other, which is still used throughout much of the world, is the Oral poliovirus vaccine (OPV).

99 children out of 100 who get the recommended vaccines will be protected from polio.

What age do you get the polio vaccine?

The vaccine, which provides inactivated doses of the virus, is usually given to children in multiple jabs.

The polio vaccine is part of the NHS routine childhood vaccination schedule. Vaccines are given at 8, 12 and 16 weeks as part of the 6-in-1 vaccines, at three years and four months as part of the  4-in-1 (DTaP/IPV) pre-school booster and at 14 years old as part of the 3-in-1 (Td/IPV) teenage booster (often administered at school).

In order to be fully vaccinated against polio, the NHS says that people must have all these vaccines.

The NHS website states: “You can have a polio vaccination at any point if you’ve never had one before, even if you’re not travelling to a country with a risk of getting polio.” 

How long does the polio vaccine last?

According to the Fit For Travel NHS website, if you’re travelling to a country with a high risk of polio, a booster dose may be needed, especially if it’s been ten years since your last jab.

“If you have not completed the minimum of 5 doses of polio-containing vaccine, you may need additional doses before you travel,” the website states.

“If you have completed the minimum of 5 doses of polio-containing vaccine, you should have a booster dose of polio-containing vaccine if it has been more than ten years since any previous doses.”

Treatment

Treatment for polio is designed to help your body fight the infection and reduce the risk of long-term impacts.

It includes bed rest, painkillers, breathing assistance and physio to prevent issues with muscles and joints.

What is the advice?

Jane Clegg, the Chief nurse for the NHS in London, said that the majority of Londoners are fully protected against polio and won’t need to take any further action. 

She explains that “the NHS will begin reaching out to parents of children aged under 5 in London who are not up to date with their Polio vaccinations to invite them to get protected.”

They added: “Meanwhile, parents can also check their child’s vaccination status in their Red Book, and people should contact their GP surgery to book a vaccination, should they or their child not be fully up to date.”

Dr Vanessa Saliba, a Consultant Epidemiologist at UKHSA, explains that: “Vaccine-derived poliovirus is rare, and the risk to the public overall is extremely low.

“Most of the UK population will be protected from vaccination in childhood, but in some communities with low vaccine coverage, individuals may remain at risk.

“We are urgently investigating to understand the extent of this transmission better, and the NHS has been asked to swiftly report any suspected cases to the UKHSA, though no cases have been reported or confirmed so far.”