A national incident was declared in June after the UK Heath Security Agency (UKHSA), working with the Medicines and Healthcare products Regulatory Agency (MHRA), detected poliovirus in sewage samples collected from the London Beckton Sewage Treatment Works.
Viral shedding via faeces is common for a number of viruses, and so the sewage system is regularly monitored for viruses as part of routine surveillance. The Government has confirmed that, ‘It is normal for 1 to 3 ‘vaccine-like’ polioviruses to be detected each year in UK sewage samples, but these have always been one-off findings that were not detected again. These previous detections occurred when an individual vaccinated overseas with the live oral polio vaccine (OPV) returned or travelled to the UK and briefly ‘shed’ traces of the vaccine-like poliovirus in their faeces.’
The alarm has been triggered after several closely related viruses were found in sewage samples taken between February and May 2022. The virus has evolved over this time and has now been classified as a ‘vaccine-derived’ poliovirus type 2 (VDPV2). This suggests there has been some spread between a limited number of individuals (most likely within an extended household), in the North and East London area. At this point no one has come forward with symptoms, and its likely infected persons do not realise they have polio.
Wild polio vs. vaccine-derived poliovirus
There are two different types of poliovirus. Wild poliovirus (WPV) is the most common and is the type of virus that has been naturally occurring for thousands of years. Vaccine-derived poliovirus (VDPV) is rarer, but numbers have been increasing in recent years due to lower levels of vaccine take up. Type 2 (VDPV2) is the type of polio associated with the UK outbreak. It is the most common type of VDPV virus.
VDPV occurs when those who have been given the live oral polio vaccine shed the virus in their faeces. In communities with low sanitation, the virus can spread. While most of the time, the spread will help to boost herd immunity by exposing more people to a mild form of the virus, in communities with low immunisation rates, the virus can take hold, spreading from one unvaccinated child to another, mutating as it goes. While this can take some time (12-18 months), eventually the virus can mutate into a form that can cause severe symptoms such as paralysis. This new form can continue to spread throughout communities, putting the unvaccinated at risk.
The only way to stop the virus spreading is to up vaccination rates. The Global Polio Eradication Initiative states the best way to prevent and stop a polio outbreak of any kind is to vaccinate children. They have developed a good animation on understanding vaccine-derived polioviruses which can be viewed via YouTube.
What is polio and is it dangerous?
Polio, or poliomyelitis, is a potentially disabling and life-threatening disease caused by the poliovirus. There is no cure for polio, but it can be prevented by vaccination. Poliovirus is very contagious and spreads easily through human-to-human contact. An infected person can spread the virus for up to six weeks and the virus can also live in contaminated faeces for a number of weeks. As around 72% of cases are asymptomatic, most people will be unaware they are spreading poliovirus.
The virus enters the body through the mouth and lives in the throat and intestines. Incubation time can be from three to 35 days. The main method of transmission is faecal-oral, when the mouth comes into contact with infected faeces. Factors can include not practicing good hand hygiene after toileting, consuming infected food or water, or young children putting contaminated items like toys in their mouths. To a lesser extent people can be infected via oral-oral transmission by coughing and sneezing.
- Approximately 72% of people show no symptoms
- In around 25% of cases, those infected will have flu like symptoms including:
- A temperature
- Extreme tiredness (fatigue)
- Neck stiffness
- Muscle and joint pain
- Muscle weakness.
- Of the remaining cases, the virus may attack nerve cells in the brain and spinal cord. Less than 1% will develop into paralytic poliomyelitis. Symptoms can include:
- Loss of reflexes
- Floppy limbs
- Severe muscle and joint pain
- Pins and needles in limbs
- Limb paralysis
- Muscle shrinkage
- Polio can be life threatening if the paralysis affects the muscles used for breathing.
- Other cases can display as non-paralytic aseptic meningitis.
- Polio sufferers are at risk of developing post-polio syndrome later in life, which can result in muscle weakness, pain or paralysis.
Who is at risk of contracting polio?
At the moment, the polio outbreak is very small and the chances of catching the virus are extremely slim. If you are vaccinated, there should be very little risk of contracting the illness, even if you are in direct contact with an infected person. However, unvaccinated children do have the highest risk. The authorities are urgently investigating the cause of the outbreak and the extent of transmission, to bring the situation swiftly under control.
Dr Vanessa Saliba, Consultant Epidemiologist at the UK Heath Security Agency (UKHSA) said, “Vaccine-derived poliovirus is rare and the risk to the public overall is extremely low. Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower. On rare occasions it can cause paralysis in people who are not fully vaccinated so if you or your child are not up to date with your polio vaccinations it’s important you contact your GP to catch up or if unsure check your Red Book. 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.”
Jane Clegg, Chief nurse for the NHS in London said, “The majority of Londoners are fully protected against Polio and won’t need to take any further action, but 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.”
Find out more about poliovirus and ways to stay safe.
Or visit the NHS website for information on polio treatment and vaccinations.