The UK Heath Security Agency (UKHSA), working with the Medicines and Healthcare products Regulatory Agency (MHRA), found poliovirus in sewage samples collected from the London Beckton Sewage Treatment Works.
The last case of wild polio contracted in the United Kingdom was confirmed in 1984. The UK was declared polio-free in 2003.
Dr Vanessa Saliba, Consultant Epidemiologist at 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.
"We are urgently investigating to better understand the extent of this transmission 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."
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.
"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."
The UKSA said that as part of routine surveillance, 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 current investigations come after several closely-related viruses were found in sewage samples taken between February and May. The virus has continued to evolve and is now 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.
The detection of a VDPV2 suggests it is likely there has been some spread between closely-linked individuals in North and East London and that they are now shedding the type 2 poliovirus strain in their faeces.
The virus has only been detected in sewage samples and no associated cases of paralysis have been reported – but investigations will aim to establish if any community transmission is occurring.
First confirmed case of Monkeypox in the northThe UK is considered by the World Health Organization to be polio-free, with low-risk for polio transmission due to the high level of vaccine coverage across the population. However, vaccine coverage for childhood vaccines has decreased nationally and especially in parts of London over the past few years, so UKHSA is urging people to check they are up to date with their vaccines.
The UKHSA says wastewater surveillance is being expanded to assess the extent of transmission and identify local areas for targeted action. Healthcare professionals have been alerted to these findings so they can promptly investigate and report anyone presenting with symptoms that could be polio, such as paralysis.